N-2

☐	Check box if the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans.
☒	Check box if any securities being registered on this Form will be offered on a delayed or continuous basis in reliance on Rule 415 under the Securities Act of 1933 (“Securities Act”), other than securities offered in connection with a dividend reinvestment plan.
☒	Check box if this Form is a registration statement pursuant to General Instruction A.2 or a post-effective amendment thereto.
☐	Check box if this Form is a registration statement pursuant to General Instruction B or a post-effective amendment thereto that will become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act.
☐	Check box if this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction B to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act.

It is proposed that this filing will become effective (check appropriate box):
☐	when declared effective pursuant to Section 8(c), or as follows:

If appropriate, check the following box:
☐	This post-effective amendment designates a new effective date for a previously filed post-effective amendment.
☐	This Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, and the Securities Act registration statement number of the earlier effective registration statement for the same offering is:
☐	This Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, and the Securities Act registration statement number of the earlier effective registration statement for the same offering is:
☐	This Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, and the Securities Act registration statement number of the earlier effective registration statement for the same offering is:

Check each box that appropriately characterizes the Registrant:
☒	Registered Closed-End Fund (closed-end company that is registered under the Investment Company Act of 1940 (“Investment Company Act”)).
☐	Business Development Company (closed-end company that intends or has elected to be regulated as a business development company under the Investment Company Act).
☐	Interval Fund (Registered Closed-End Fund or a Business Development Company that makes periodic repurchase offers under Rule 23c-3 under the Investment Company Act).
☒	A.2 Qualified (qualified to register securities pursuant to General Instruction A.2 of this Form).
☐	Well-Known Seasoned Issuer (as defined by Rule 405 under the Securities Act).
☐	Emerging Growth Company (as defined by Rule 12b-2 under the Securities Exchange Act of 1934 (“Exchange Act”).
☐	If an Emerging Growth Company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of Securities Act.
☐	New Registrant (registered or regulated under the Investment Company Act for less than 12 calendar months preceding this filing).

Subject to Completion

Preliminary Prospectus dated September 2, 2022

PIMCO Municipal Income Fund

Base Prospectus

[ ]

THE INFORMATION IN THIS PROSPECTUS IS NOT COMPLETE AND MAY BE CHANGED. WE MAY NOT SELL THESE SECURITIES UNTIL THE REGISTRATION STATEMENT FILED WITH THE SECURITIES AND EXCHANGE COMMISSION IS EFFECTIVE. THIS PROSPECTUS IS NOT AN OFFER TO SELL THESE SECURITIES AND IT IS NOT SOLICITING AN OFFER TO BUY THESE SECURITIES IN ANY JURISDICTION WHERE THE OFFER OR SALE IS NOT PERMITTED.

PIMCO Municipal Income Fund

$[ ]	Common Shares
PIMCO Municipal Income Fund	PMF

Neither the U.S. Securities and Exchange Commission nor the U.S. Commodity Futures Trading Commission has approved or disapproved of these securities or determined that this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

As permitted by regulations adopted by the Securities and Exchange Commission, paper copies of the Fund’s annual and semi-annual shareholder reports will no longer be sent by mail, unless you specifically request paper copies of the reports from the Fund or from your financial intermediary, such as a broker-dealer or bank. Instead, the reports will be made available on the Fund’s website, pimco.com/literature, and you will be notified by mail each time a report is posted and provided with a website link to access the report.

If you already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive shareholder reports and other communications from the Fund electronically by visiting pimco.com/edelivery or by contacting your financial intermediary, such as a broker-dealer or bank.

You may elect to receive all future reports in paper free of charge. If you own these shares through a financial intermediary, such as a broker-dealer or bank, you may contact your financial intermediary to request that you continue to receive paper copies of your shareholder reports. If you invest directly with the Fund, you can inform the Fund that you wish to continue receiving paper copies of your shareholder reports by calling 844.337.4626. Your election to receive reports in paper will apply to all funds held with the fund complex if you invest directly with the Fund or to all funds held in your account if you invest through a financial intermediary, such as a broker-dealer or bank.

The Fund. PIMCO Municipal Income Fund (the “Fund”) is a diversified, closed-end management investment company that commenced operations on June 29, 2011, following the initial public offering of its common shares.

The Fund’s common shares of beneficial interest, par value $0.00001 per share (the “Common Shares”) are listed on the New York Stock Exchange (“NYSE”) under the symbol PMF. The last reported sale price of the Common Shares, as reported by the NYSE on [ ] was $[ ] per Common Share. The net asset value (“NAV”) of the Common Shares at the close of business on [ ] was $[ ] per Common Share.

Investment Objectives. The Fund seeks to provide current income exempt from federal income tax.

Investment Strategy. Under normal circumstances, the Fund expects to invest at least 90% of its net assets in municipal bonds which pay interest that, in the opinion of bond counsel to the issuer (or on the basis of other authority believed by PIMCO to be reliable), is exempt from regular federal income taxes (i.e., excluded from gross income for federal income tax purposes but not necessarily exempt from the federal alternative minimum tax). Subject to its other investment policies, the Fund may invest up to 20% of its total assets in investments the interest from which is subject to the federal alternative minimum tax.

Investment in the Fund’s Common Shares involves substantial risks arising from, among other strategies, the Fund’s ability to invest in debt instruments that are, at the time of purchase, rated below investment grade (below Baa3 by Moody’s Investors Service, Inc. or below BBB- by either S&P Global Ratings or Fitch, Inc.) or unrated but determined by PIMCO to be of comparable quality, the Fund’s exposure to foreign (including emerging markets) securities and currencies and to mortgage-related and other asset-backed securities, and the Fund’s use of leverage. Debt securities of below investment grade quality are regarded as having predominantly speculative characteristics with respect to capacity to pay interest and to repay principal, and are commonly referred to as “high yield” securities or “junk bonds.” The Fund’s exposure to municipal securities means it is particularly subject to the risk that a municipal issuer will be unable to make timely payments of interest and principal, which risk will generally be higher during general economic downturns and may be adversely impacted by litigation, legislation or political events, or by the bankruptcy of the issuer. Before investing in the Common Shares, you should read the discussion of the principal risks of investing in the Fund in “ Principal Risks of the Fund.” Certain of these risks are summarized in “Prospectus Summary—Principal Risks of the Fund.” The Fund cannot assure you that it will achieve its investment objectives, and you could lose all of your investment in the Fund.

Portfolio Contents. Under normal circumstances, the Fund expects to invest at least 90% of its net assets in municipal bonds which pay interest that, in the opinion of bond counsel to the issuer (or on the basis of other authority believed by PIMCO to be reliable), is exempt from regular federal income taxes (i.e., excluded from gross income for federal income tax purposes but not necessarily exempt from the federal alternative minimum tax). Subject to its other investment policies, the Fund may invest up to 20% of its total assets in investments the interest from which is subject to the federal alternative minimum tax.

The municipal bonds in which the Fund invests are generally issued by a U.S. state or territory, a city in a U.S. state or territory, or a political subdivision, agency, authority, or instrumentality of such state, territory or city.

Also included within the general category of municipal bonds in which the Fund may invest are participations in lease obligations.

The Fund invests at least 80% of its net assets in municipal bonds that are, at the time of purchase, rated “investment grade” by at least one of Moody’s Investors Service, Inc (“Moody’s”), S&P Global Ratings (“S&P”) or Fitch, Inc. (“Fitch”), or unrated but determined by PIMCO to be of comparable quality. “Investment grade” means a rating, in the case of Moody’s, of Baa3 or higher, or in the case of S&P and Fitch, of BBB- or higher.

The Fund may invest up to 20% of its net assets in municipal bonds that are, at the time of investment, rated Ba or B or lower by Moody’s, BB or B or lower by S&P or Fitch or that are unrated but judged to be of comparable quality by PIMCO. In the event that ratings services assign different ratings to the same security, PIMCO will use the highest rating as the credit rating for that security. Bonds of below investment grade quality are regarded as having predominantly speculative characteristics with respect to capacity to pay interest and repay principal and are commonly referred to as “junk bonds.” Bonds in the lowest investment grade category may also be considered to possess some speculative characteristics.

The Fund may invest in “structured” notes, which are privately negotiated debt obligations where the principal and/or interest is determined by reference to the performance of a benchmark asset or market, such as selected securities or an index of securities, or the differential performance of two assets or markets, such as indices reflecting taxable and tax-exempt bonds. The Fund may do so for the purpose of reducing the interest rate sensitivity of the Fund’s portfolio (and thereby decreasing the Fund’s exposure to interest rate risk).

The Fund may purchase municipal bonds that are additionally secured by insurance, bank credit agreements, or escrow accounts. The credit quality of companies which provide such credit enhancements will affect the value and overall credit risk posed by investments in such securities. Although the insurance feature reduces certain financial risks, the premiums for insurance and the higher market price paid for insured obligations may reduce the Fund’s income and returns.

The Fund may buy and sell municipal bonds on a when-issued, delayed delivery or forward commitment basis, making payment or taking delivery at a later date. The Fund may invest in floating rate debt instruments (“floaters”), including inverse floaters, and engage in credit spread trades.

The Fund may invest in trust certificates issued in tender option bond (“TOB”) programs. In these programs, a trust typically issues two classes of certificates and seeks to use the proceeds to purchase municipal securities having longer maturities and bearing interest at a higher fixed interest rate than prevailing short-term tax-exempt rates. Service providers of such trusts may have recourse against the Fund in certain cases.

The Fund may also invest up to 10% of its total assets in securities of other open- or closed-end investment companies that invest primarily in municipal bonds of the types in which the Fund may invest directly. The Fund may invest in other investment companies either during periods when it has large amounts of uninvested cash, during periods when there is a shortage of attractive, high-yielding municipal bonds available in the market, or when PIMCO believes share prices of other investment companies offer attractive values. The Fund may invest in investment companies that are advised by PIMCO or its affiliates to the extent permitted by applicable law and/or pursuant to exemptive relief from the Securities and Exchange Commission. As a shareholder of an investment company, the Fund will bear its ratable share of that investment company’s expenses and would remain subject to payment of the Fund’s management fees and other expenses with respect to assets so invested.

The Fund generally intends to invest primarily in municipal bonds with longer-term maturities (for example, 15-30 years), but may invest in bonds of any maturity and otherwise seek a shorter average weighted maturity of its portfolio.

The Fund may purchase and sell (write) a variety of derivatives, such as put options and call options on securities, short sales, swap agreements, and securities indexes, and enter into interest rate and index futures contracts and purchase and sell options on such futures contracts for hedging purposes or as part of its overall investment strategy. The Fund also may enter into swap agreements with respect to interest rates and indexes of securities. If other types of financial instruments, including other types of options, futures contracts, or futures options are traded in the future, the Fund may also use those instruments.

The Fund may invest up to 20% of its net assets in securities which are illiquid at the time of investment (i.e., any investment that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment).

In connection with rating the Fund’s outstanding auction rate preferred shares of beneficial interest (“ARPS”) and remarketable variable rate munifund term preferred shares of beneficial interest (“RVMTP Shares” and, together with the ARPS and any other preferred shares the Fund may have outstanding, the “Preferred Shares”), Moody’s and Fitch impose asset coverage tests and other restrictions that may limit the Fund’s ability to engage in certain of the transactions described above.

Leverage. The Fund currently utilizes leverage principally through its outstanding Preferred Shares and floating rate notes issued in TOB transactions. The Fund may also enter into transactions other than those noted above that may give rise to a form of leverage including, among others, futures contracts, options on futures contracts, forward contracts, or any interest rate, securities-related or other hedging instrument, including swap agreements and other derivative instruments. The Fund may also determine to issue other types of Preferred Shares or determine to decrease the leverage it currently maintains by redeeming its outstanding Preferred Shares or unwinding TOBs and may or may not determine to replace such leverage through other sources. If the Fund issues additional Preferred Shares in the future, all costs and expenses relating to the issuance and ongoing maintenance of the Preferred Shares will be borne by the holders of Common Shares (“Common Shareholders”), and these costs and expenses may be significant.

The amount of leverage that the Fund uses may change, but total leverage is not normally expected to exceed 50% of the Fund’s total assets.

Depending upon market conditions and other factors, the Fund may or may not determine to add leverage following an offering to maintain or increase the total amount of leverage (as a percentage of the Fund’s total assets) that the Fund currently maintains, taking into account the additional assets raised through the issuance of Common Shares in such offering. The Fund utilizes certain kinds of leverage, including, without limitation, Preferred Shares and TOBs, opportunistically and may choose to increase or decrease, or eliminate entirely, its use of such leverage over time and from time to time based on PIMCO’s assessment of the yield curve environment, interest rate trends, market conditions and other factors. If the Fund determines to add leverage following an offering, it is not possible to predict with accuracy the precise amount of leverage that would be added, in part because it is not possible to predict the number of Common Shares that ultimately will be sold in an offering or series of offerings. To the extent that the Fund does not add additional leverage following an offering, the Fund’s total amount of leverage as a percentage of its total assets will decrease, which could result in a reduction of investment income available for distribution to Common Shareholders.

Additional Information. This prospectus is part of a registration statement that the Fund has filed with the U.S. Securities and Exchange Commission (the “SEC”) using the “shelf” registration process. Under the shelf registration process, the Fund may offer, from time to time, in one or more offerings, up to $[ ] Common Shares on terms to be determined at the time of the offering. This prospectus provides you with a general description of the Common Shares that the Fund may offer. Each time the Fund uses this prospectus to offer Common Shares, the Fund will provide a prospectus supplement that will contain specific information about the terms of that offering. The prospectus supplement may also add, update or change information contained in this prospectus. You should read this prospectus and the applicable prospectus supplement, which contain important information about the Fund, carefully before you invest in the Common Shares. Common Shares may be offered directly to one or more purchasers, through agents designated from time to time by the Fund, or to or through underwriters or dealers. The prospectus supplement relating to an offering will identify any agents, underwriters or dealers involved in the sale of Common Shares, and will set forth any applicable purchase price, fee, commission or discount arrangement between the Fund and its agents or underwriters, or among the Fund’s underwriters, or the basis upon which such amount may be calculated. See “Plan of Distribution.” The Fund may not sell any Common Shares

iii

through agents, underwriters or dealers without delivery or deemed delivery of a prospectus supplement describing the method and terms of the particular offering of the Common Shares. You should retain this prospectus and any prospectus supplement for future reference. A Statement of Additional Information, dated [ ], 2022, containing additional information about the Fund has been filed with the SEC and is incorporated by reference in its entirety into this prospectus. You may request a free copy of the Statement of Additional Information, request the Fund’s most recent annual and semiannual reports, request information about the Fund and make shareholder inquiries by calling toll-free (844)-337-4626 or by writing to the Fund at c/o Pacific Investment Management Company LLC, 1633 Broadway, New York, New York 10019. The Fund’s Statement of Additional Information and most recent annual and semiannual reports are available, free of charge, on the Fund’s website (https://www.pimco.com/prospectuses). You can obtain the same information, free of charge, from the SEC’s website (http://www.sec.gov).

The Common Shares do not represent a deposit or obligation of, and are not guaranteed or endorsed by, any bank or other insured depository institution, and are not federally insured by the Federal Deposit Insurance Corporation, the Federal Reserve Board or any other government agency.

The Fund has not authorized anyone to provide you with information other than that contained or incorporated by reference in this prospectus or any applicable prospectus supplement, and any free writing prospectus that the Fund distributes. The Fund does not take any responsibility for, and does not provide any assurances as to the reliability of, any other information that others may give you. The Fund is not making an offer of these securities in any jurisdiction where the offer is not permitted. You should not assume that the information contained in this prospectus or any applicable prospectus supplement is accurate as of any date other than the date on the front hereof or thereof. The Fund’s business, financial condition, results of operations and prospects may have changed since that date.

Table of Contents

	Page
Prospectus Summary	1
Summary of Fund Expenses	18
Financial Highlights	19
Use of Proceeds	20
The Fund	20
Investment Objective and Policies	20
Use of Leverage	28
Principal Risks of the Fund	30
How the Fund Manages Risk	46
Management of the Fund	47
Net Asset Value	49
Distributions	50
Dividend Reinvestment Plan	51
Description of Capital Structure	51
Plan of Distribution	58
Market and Net Asset Value Information	59
Anti-Takeover and Other Provisions in the Declaration of Trust and Bylaws	60
Repurchase of Common Shares; Conversion to Open-End Fund	61
Tax Matters	62
Custodian and Transfer Agent	64
Independent Registered Public Accounting Firm	64
Legal Matters	64
Incorporation by Reference	64
Appendix A - Description of Securities Ratings	A-1

You should rely only on the information contained or incorporated by reference in this prospectus and any related prospectus supplement. The Fund has not authorized any other person to provide you with inconsistent information. If anyone provides you with inconsistent information, you should not assume that the Fund has authorized or verified it. The Fund is not making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should not assume that the information contained in this prospectus or any prospectus supplement is accurate as of any date other than the dates on their respective front covers. The Fund’s business, financial condition, results of operations and prospects may have changed since the date of this prospectus or the date of any prospectus supplement.

PIMCO Municipal Income Fund

Prospectus Summary

This is only a summary. This summary may not contain all of the information that you should consider before investing in the Fund’s common shares of beneficial interest, par value $0.00001 per share (the “Common Shares”). You should review the more detailed information contained in this prospectus and in any related prospectus supplement and in the Statement of Additional Information, especially the information set forth under the heading “Principal Risks of the Fund.”

The Fund

PIMCO Municipal Income Fund (the “Fund”) is a diversified, closed-end management investment company. The Fund commenced operations on June 29, 2001, following the initial public offering of its Common Shares.

The Common Shares are listed on the New York Stock Exchange (“NYSE”) under the symbol “PMF.” As of June 30, 2022 the net assets of the Fund attributable to Common Shares were $[ ] and the Fund had outstanding [ ] Common Shares, 6,668 auction rate preferred shares of beneficial interest (“ARPS”) and 233 remarketable variable rate munifund term preferred shares of beneficial interest (“RVMTP Shares” and, together with the ARPS and any other preferred shares the Fund may have outstanding, the “Preferred Shares”). The last reported sale price of the Common Shares, as reported by the NYSE on [ ] was $[ ] per Common Share. The net asset value (“NAV”) of the Common Shares at the close of business on [ ] was $[ ] per Common Share. See “Description of Capital Structure.”

The Offering

The Fund may offer, from time to time, in one or more offerings, Common Shares on terms to be determined at the time of the offering. The Common Shares may be offered at prices and on terms to be set forth in one or more prospectus supplements. You should read this prospectus and the applicable prospectus supplement carefully before you invest in the Common Shares. Common Shares may be offered directly to one or more purchasers, through agents designated from time to time by the Fund, or to or through underwriters or dealers. The prospectus supplement relating to an offering will identify any agents, underwriters or dealers involved in the sale of Common Shares, and will set forth any applicable purchase price, fee, commission or discount arrangement between the Fund and its agents or underwriters, or among the Fund’s underwriters, or the basis upon which such amount may be calculated. See “Plan of Distribution.” The Fund may not sell any Common Shares through agents, underwriters or dealers without delivery or deemed delivery of a prospectus supplement describing the method and terms of the particular offering of the Common Shares.

Use of Proceeds

Fund, depending on the amount and timing of proceeds available to the Fund as well as the availability of investments consistent with the Fund’s investment objective and policies, and except to the extent proceeds are held in cash to pay dividends or expenses, or for temporary defensive purposes. See “Use of Proceeds.”

Investment Objective and Policies

The Fund seeks to provide current income exempt from federal income tax. In pursuing the Fund’s investment objective, the Fund’s investment manager, Pacific Investment Management Company LLC (“PIMCO or the “Investment Manager”), also seeks to preserve and enhance the value of the Fund’s holdings relative to the municipal bond market generally, using proprietary analytical models that test and evaluate the sensitivity of those holdings to changes in interest rates and yield relationships. The Fund cannot assure you that it will achieve its investment objective, and you could lose all of your investment in the Fund.

Portfolio Investment Strategies

Under normal circumstances, the Fund expects to invest at least 90% of its net assets in municipal bonds which pay interest that, in the opinion of bond counsel to the issuer (or on the basis of other authority believed by the PIMCO to be reliable), is exempt from regular federal income taxes (i.e., excluded from gross income for federal income tax purposes but not necessarily exempt from the federal alternative minimum tax). Subject to its other investment policies, the Fund may invest up to 20% of its total assets in investments the interest from which is subject to the federal alternative minimum tax.

The Fund invests at least 80% of its net assets in municipal bonds that at the time of investment are investment grade quality. Investment grade quality bonds are bonds rated within the four highest grades (Baa by Moody’s or BBB or better by S&P or Fitch), or bonds that are unrated but determined to be of comparable quality by PIMCO. The Fund may invest up to 20% of its net assets in municipal bonds that are, at the time of investment, rated Ba/BB or B or lower by Moody’s, S&P or Fitch or that are unrated but judged to be of comparable quality by PIMCO. Bonds of below investment grade quality are regarded as having predominantly speculative characteristics with respect to capacity to pay interest and repay principal, and are commonly referred to as “junk bonds.” Bonds in the lowest investment grade category may also be considered to possess some speculative characteristics.

The Fund’s investment in municipal bonds may be based on PIMCO’s belief that they have attractive yield and/or total return potential. The Fund attempts to produce returns relative to the municipal bond market generally by prudent selection of municipal bonds. The Fund may invest in bonds associated with a particular municipal market sector (for example, electric utilities), issued by a particular municipal issuer, or having particular structural characteristics, that PIMCO believes may be undervalued. PIMCO may purchase such a bond for the Fund’s portfolio because it represents a market sector or issuer that PIMCO considers undervalued. For example, municipal bonds of particular types (e.g., hospital bonds, industrial revenue bonds or bonds issued by a particular

1 PIMCO Municipal Income Fund | Base Prospectus

Base Prospectus

municipal issuer) could be undervalued if there is a temporary excess of supply in that market sector, or because of a general decline in the market price of municipal bonds of the market sector for reasons that do not apply to the particular municipal bonds that are considered undervalued.

Portfolio Contents

Also included within the general category of municipal bonds in which the Fund may invest are participations in lease obligations.

The Fund may invest in trust certificates issued in tender option bond (“TOB”) programs. In these programs, a trust typically issues two classes of certificates, floating rate certificates (“TOB Floaters”) and residual interest certificates (“TOB Residuals”), and seeks to use the proceeds to purchase municipal securities having longer maturities and bearing interest at a higher fixed interest rate than prevailing short-term tax-exempt rates. Service providers of such trusts may have recourse against the Fund in certain cases, such as if the Fund holds recourse TOB Residuals. The Fund may invest in both non-recourse and recourse TOB Residuals to leverage its portfolio.

in the market, or when PIMCO believes share prices of other investment companies offer attractive values. The Fund may invest in investment companies that are advised by PIMCO or its affiliates to the extent permitted by applicable law and/or pursuant to exemptive relief from the Securities and Exchange Commission. As a shareholder of an investment company, the Fund will bear its ratable share of that investment company’s expenses and would remain subject to payment of the Fund’s management fees and other expenses with respect to assets so invested.

The Fund has outstanding auction rate preferred shares of beneficial interest (“ARPS”) and remarketable variable rate munifund term preferred shares of beneficial interest (“RVMTP Shares” and, together with the ARPS and any other preferred shares the Fund may have outstanding, the “Preferred Shares”). In connection with rating the Fund’s Preferred Shares, Moody’s and Fitch, as applicable, impose specific asset coverage tests and other limitations and restrictions that may limit the Fund’s ability to engage in certain of the transactions described above. In addition, failure to comply with these limitations and restrictions could, among other things, preclude the Fund from declaring or paying dividend or distributions.

Temporary Defensive Investments. Upon PIMCO’s recommendation, temporarily or for defensive purposes and in order to keep the Fund’s cash fully invested, the Fund may invest up to 100% of its net assets in high quality, short-term investments, including U.S. government, mortgage-backed and corporate debt securities that may be either tax-exempt or taxable. To the extent the Fund invests in taxable short-term investments, the Fund will not at such times be in a position to achieve its investment objective.

Leverage

The Fund currently utilizes leverage principally through its outstanding Preferred Shares and floating rate notes issued in TOB transactions. The Fund may also enter into transactions other than those noted above that may give rise to a form of leverage including, among others, futures contracts, options on futures contracts, forward contracts, or any interest rate, securities-related or other hedging instrument, including swap agreements and other derivative instruments. The Fund may also determine to issue other types of Preferred Shares or determine to

[ ] | Base Prospectus 2

PIMCO Municipal Income Fund

decrease the leverage it currently maintains by redeeming or tendering its outstanding Preferred Shares or unwinding TOBs and may or may not determine to replace such leverage through other sources.

The amount of leverage that the Fund uses may change, but total leverage is not normally expected to exceed 50% of the Fund’s total assets.

The Fund may also enter into transactions other than those noted above that may give rise to a form of leverage including, among others, futures and forward contracts (including foreign currency exchange contracts), total return swaps and other derivative transactions, loans of portfolio securities, short sales, when-issued, delayed delivery and forward commitment transactions and selling credit default swaps.

Depending upon market conditions and other factors, the Fund may or may not determine to add leverage following an offering to maintain or increase the total amount of leverage (as a percentage of the Fund’s total assets) that the Fund currently maintains, taking into account the additional assets raised through the issuance of Common Shares in such offering. The Fund utilizes certain kinds of leverage, including, without limitation, Preferred Shares and TOBs, opportunistically and may choose to increase or decrease, or eliminate entirely, its use of such leverage over time and from time to time based on PIMCO’s assessment of the yield curve environment, interest rate trends, market conditions and other factors. The Fund may also determine to decrease the leverage it currently maintains by redeeming its outstanding Preferred Shares or unwinding TOBs and may or may not determine to replace such leverage through other sources. If the Fund determines to add leverage following an offering, it is not possible to predict with accuracy the precise amount of leverage that would be added, in part because it is not possible to predict the number of Common Shares that ultimately will be sold in an offering or series of offerings. To the extent that the Fund does not add additional leverage following an offering, the Fund’s total amount of leverage as a percentage of its total assets will decrease, which could result in a reduction of investment income available for distribution to Common Shareholders.

The Fund also may borrow money for temporary administrative purposes, to add leverage to the portfolio or for the settlement of securities transactions which otherwise might require untimely dispositions of portfolio securities held by the Fund.

Please see “Use of Leverage” and “Principal Risks of the Fund—Leverage Risk” in the body of this prospectus for additional information regarding leverage and related risks.

Investment Manager

Pacific Investment Management Company LLC (“PIMCO” or the “Investment Manager”) serves as the investment manager of the Fund. Subject to the supervision of the Board of Trustees of the Fund (the “Board”), PIMCO is responsible for managing the investment activities of the Fund and the Fund’s business affairs and other administrative matters. David Hammer is primarily responsible for the day-to-day management of the Fund.

The Investment Manager receives an annual fee from the Fund, payable monthly, in an amount equal to 0.705% of the Fund’s average daily net asset value including daily net assets attributable to any Preferred Shares. Average daily net assets means an average of all the determinations of the Fund’s net assets (including net assets attributable to Preferred Shares) during a given month at the close of business on each business day during such month. PIMCO is located at 650 Newport Center Drive, Newport Beach, CA, 92660. Organized in 1971, PIMCO provides investment management and advisory services to private accounts of institutional and individual clients and to registered investment companies. PIMCO is a majority-owned indirect subsidiary of Allianz SE, a publicly traded European insurance and financial services company. As of June 30, 2022, PIMCO had approximately $1.82 trillion of assets under management. As of June 30, 2022, PIMCO had $ $1.43 trillion of third-party assets under management.

Dividends and Distributions

The Fund generally distributes each year all of its net investment income and net short-term capital gains. In addition, at least annually, the Fund generally distributes net realized long-term capital gains not previously distributed, if any. The Fund may distribute less than the entire amount of net investment income earned in a particular period. The undistributed net investment income would be available to supplement future distributions. As a result, the distributions paid by the Fund for any particular monthly period may be more or less than the amount of net investment income actually earned by the Fund during the period. The tax treatment and characterization of the Fund’s distributions may vary significantly from time to time because of the varied nature of the Fund’s investments.

3 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

from which a distribution is paid, to the close of the period as of which it is paid, in reference to its internal accounting records and related accounting practices. If, based on such accounting records and practices, it is estimated that a particular distribution does not include capital gains or paid-in surplus or other capital sources, a Section 19 Notice generally would not be issued. It is important to note that differences exist between the Fund’s daily internal accounting records and practices, the Fund’s financial statements presented in accordance with U.S. GAAP, and recordkeeping practices under income tax regulations. Accordingly, among other consequences, it is possible that the Fund may not issue a Section 19 Notice in situations where the Fund’s financial statements prepared later and in accordance with U.S. GAAP and/or the final tax character of those distributions might later report that the sources of those distributions included capital gains and/or a return of capital.

The tax characterization of the Fund’s distributions made in a taxable year cannot finally be determined until at or after the end of such taxable year. As a result, there is a possibility that the Fund may make total distributions during a taxable year in an amount that exceeds the Fund’s net investment income and net realized capital gains (as reduced by any capital loss carry-forwards) for the relevant year. For example, the Fund may distribute amounts early in the year that are derived from short-term capital gains, but incur net short-term capital losses later in the year, thereby offsetting short-term capital gains out of which the Fund has already made distributions. In such a situation, the amount by which the Fund’s total distributions exceed net investment income and net realized capital gains would generally be treated as a tax-free return of capital up to the amount of a shareholder’s tax basis in his or her Common Shares, with any amounts exceeding such basis treated as gain from the sale of Common Shares. In general terms, a return of capital would occur where the Fund distribution (or portion thereof) represents a return of a portion of your investment, rather than net income or capital gains generated from your investment during a particular period. Although return of capital distributions are not taxable, such distributions would reduce the basis of a shareholder’s Common Shares and therefore may increase a shareholder’s capital gains, or decrease a shareholder’s capital loss, upon a sale of Common Shares, thereby potentially increasing a shareholder’s tax liability. The Fund will prepare and make available to shareholders detailed tax information with respect to the Fund’s distributions annually. See “Tax Matters.”

The 1940 Act currently limits the number of times the Fund may distribute long-term capital gains in any tax year, which may increase the variability of the Fund’s distributions and result in certain distributions being comprised more or less heavily than others of long-term capital gains currently eligible for favorable income tax rates. The Fund, as well as several other PIMCO-managed closed end funds, has received exemptive relief from the SEC permitting it to make a greater number of capital gains distributions to holders of the ARPS than would otherwise be permitted by Section 19(b) of the 1940 Act and Rule 19b-1 under the 1940 Act.

Unless a Common Shareholder elects to receive distributions in cash, all distributions of Common Shareholders whose shares are registered with the plan agent will be automatically reinvested in additional Common Shares of the Fund under the Fund’s Dividend Reinvestment Plan. For more information on the Fund’s dividends and distributions, see “Distributions” and “Dividend Reinvestment Plan.”

Custodian and Transfer Agent

State Street Bank and Trust Company serves as custodian of the Fund’s assets and also provides certain fund accounting and sub-administrative services to the Investment Manager on behalf of the Fund. American Stock Transfer & Trust Company, LLC serves as the Fund’s transfer agent and dividend disbursement agent. See “Custodian and Transfer Agent.”

Listing

The Fund’s outstanding Common Shares are listed on the NYSE under the trading or “ticker” symbol “PMF”, as will be the Common Shares offered in this prospectus, subject to notice of issuance.

Market Price of Shares

Shares of closed-end investment companies frequently trade at prices lower than NAV. Shares of closed-end investment companies have during some periods traded at prices higher than NAV and during other periods traded at prices lower than NAV. The Fund cannot assure you that Common Shares will trade at a price equal to or higher than NAV in the future. Proceeds from the sale of Common Shares of an offering will be reduced by any sales load and/or commissions and the amount of offering expenses paid or reimbursed by the Fund. The Fund (and not PIMCO) bears all offering expenses. See “Use of Proceeds.” In addition to NAV, market price may be affected by factors relating to the Fund such as dividend levels and stability (which will in turn be affected by Fund expenses, including the costs of any leverage used by the Fund, levels of interest payments by the Fund’s portfolio holdings, levels of appreciation/depreciation of the Fund’s portfolio holdings, regulation affecting the timing and character of Fund distributions and other factors), portfolio credit quality, liquidity, call protection, market supply and demand and similar factors relating to the Fund’s portfolio holdings. See “Use of Leverage,” “Principal Risks of the Fund,” “Description of Capital Structure” and “Repurchase of Common Shares; Conversion to Open-End Fund” in this prospectus, and see “Repurchase of Common Shares; Conversion to Open-End Fund” in the Statement of Additional Information. The Common Shares are designed for long-term investors and should not be treated as trading vehicles.

Principal Risks of the Fund

The following is a summary of the principal risks associated with an investment in Common Shares of the Fund. Investors should also refer to “Principal Risks of the Fund” in this prospectus and “Investment Objective and Policies” in the Statement of Additional Information for a more detailed explanation of these and other risks associated with investing in the Fund.

[ ] | Base Prospectus 4

PIMCO Municipal Income Fund

Market Discount Risk

The price of the Fund’s Common Shares will fluctuate with market conditions and other factors. If you sell your Common Shares, the price received may be more or less than your original investment. The Common Shares are designed for long-term investors and should not be treated as trading vehicles. Shares of closed-end management investment companies frequently trade at a discount from their NAV. The Common Shares may trade at a price that is less than the offering price for Common Shares issued pursuant to an offering. This risk may be greater for investors who sell their Common Shares relatively shortly after completion of an offering. The sale of Common Shares by the Fund (or the perception that such sales may occur), particularly if sold at a discount to the then current market price of the Common Shares, may have an adverse effect on the market price of the Common Shares.

Market Risk

The market price of securities owned by the Fund may go up or down, sometimes rapidly or unpredictably. Securities may decline in value due to factors affecting securities markets generally or particular industries represented in the securities markets. The value of a security may decline due to general market conditions that are not specifically related to a particular company, such as real or perceived adverse economic conditions, changes in the general outlook for corporate earnings, changes in interest or currency rates, adverse changes to credit markets or adverse investor sentiment generally. The value of a security may also decline due to factors that affect a particular industry or industries, such as labor shortages or increased production costs and competitive conditions within an industry. During a general downturn in the securities markets, multiple asset classes may decline in value simultaneously. Equity securities generally have greater price volatility than fixed income securities. Credit ratings downgrades may also negatively affect securities held by the Fund. Even when markets perform well, there is no assurance that the investments held by the Fund will increase in value along with the broader market.

In addition, market risk includes the risk that geopolitical and other events will disrupt the economy on a national or global level. For instance, war, terrorism, market manipulation, government defaults, government shutdowns, political changes or diplomatic developments, public health emergencies (such as the spread of infectious diseases, pandemics and epidemics) and natural/environmental disasters can all negatively impact the securities markets, which could cause the Fund to lose value. These events could reduce consumer demand or economic output, result in market closures, travel restrictions or quarantines, and significantly adversely impact the economy. The current contentious domestic political environment, as well as political and diplomatic events within the United States and abroad, such as presidential elections in the United States or abroad or the U.S. government’s inability at times to agree on a long-term budget and deficit reduction plan, has in the past resulted, and may in the future result, in a government shutdown or otherwise adversely affect the U.S. regulatory landscape, the general market environment and/or investor sentiment, which could have an adverse impact on the Fund’s investments and operations. Additional and/ or prolonged U.S. federal government

shutdowns may affect investor and consumer confidence and may adversely impact financial markets and the broader economy, perhaps suddenly and to a significant degree. Governmental and quasi-governmental authorities and regulators throughout the world have previously responded to serious economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or sudden reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. Any market disruptions could also prevent the Fund from executing advantageous investment decisions in a timely manner. Funds that have focused their investments in a region enduring geopolitical market disruption will face higher risks of loss. Thus, investors should closely monitor current market conditions to determine whether the Fund meets their individual financial needs and tolerance for risk.

Recently, there have been signs of inflationary price movements. As such, fixed income securities markets may experience heightened levels of interest rate, volatility and liquidity risk. Any interest rate increases in the future could cause the value of any fund, such as the Fund, that invests in fixed income securities to decrease.

Municipal Bond Risk

The ability of municipal issuers to make timely payments of interest and principal may be diminished during general economic downturns, by litigation, legislation or political events, or by the bankruptcy of the issuer. Laws, referenda, ordinances or regulations enacted in the future by Congress or state legislatures or the applicable governmental entity could extend the time for payment of principal and/or interest, or impose other constraints on enforcement of such obligations, or on the ability of municipal issuers to levy taxes. Issuers of municipal securities also might seek protection under the bankruptcy laws. In the event of bankruptcy of such an issuer, the Fund could experience delays in collecting principal and interest and the Fund may not, in all circumstances, be able to collect all principal and interest to which it is entitled. To enforce its rights in the event of a default in the payment of interest or repayment of principal, or both, the Fund may take possession of and manage the assets securing the issuer’s obligations on such securities, which may increase the Fund’s operating expenses.

The Fund may invest in revenue bonds, which are typically issued to fund a wide variety of capital projects including electric, gas, water and sewer systems; highways, bridges and tunnels; port and airport facilities; colleges and universities; and hospitals. Because the principal security for a revenue bond is generally the net revenues derived from a particular facility or group of facilities or, in some cases, from the proceeds of a special excise or other specific revenue source, there is no guarantee that the particular project will generate enough revenue to pay its obligations, in which case the Fund’s performance may be adversely affected.

5 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

The Fund may invest in taxable municipal bonds, such as Build America Bonds. Build America Bonds are tax credit bonds created by the American Recovery and Reinvestment Act of 2009, which authorized state and local governments to issue Build America Bonds as taxable bonds in 2009 and 2010, without volume limitations, to finance any capital expenditures for which such issuers could otherwise issue traditional tax-exempt bonds. The Fund’s investments in Build America Bonds or similar taxable municipal bonds will result in taxable income and the Fund may elect to pass through to holders of the Fund’s common shares (“Common Shares”) the corresponding tax credits. The tax credits can generally be used to offset federal income taxes and the alternative minimum tax, but such credits are generally not refundable. Taxable municipal bonds involve similar risks as tax-exempt municipal bonds, including credit and market risk.

Municipal securities are also subject to interest rate, credit, and liquidity risk, which are discussed generally elsewhere in this section, and elaborated upon below with respect to municipal bonds.

◾

Interest Rate Risk. The value of municipal securities, similar to other fixed income securities, will likely drop as interest rates rise in the general market. Conversely, when rates decline, bond prices generally rise.

◾

Credit Risk. The risk that a borrower may be unable to make interest or principal payments when they are due. A fund that invests in municipal securities relies on the ability of the issuer to service its debt. This subjects the Fund to credit risk in that the municipal issuer may be fiscally unstable or exposed to large liabilities that could impair its ability to honor its obligations. Municipal issuers with significant debt service requirements, in the near-to mid-term; unrated issuers and those with less capital and liquidity to absorb additional expenses may be most at risk. To the extent the Fund invests in lower quality or high yield municipal securities, it may be more sensitive to the adverse credit events in the municipal market. The treatment of municipalities in bankruptcy is more uncertain, and potentially more adverse to debt holders, than for corporate issues.

◾

Liquidity Risk. The risk that investors may have difficulty finding a buyer when they seek to sell, and therefore, may be forced to sell at a discount to the market value. Liquidity may sometimes be impaired in the municipal market and because the Fund primarily invests in municipal securities, it may find it difficult to purchase or sell such securities at opportune times. Liquidity can be impaired due to interest rate concerns, credit events, or general supply and demand imbalances. Depending on the particular issuer and current economic conditions, municipal securities could be deemed more volatile investments.

In addition to general municipal market risks, different municipal sectors may face different risks. For instance, general obligation bonds are secured by the full faith, credit, and taxing power of the municipality issuing the obligation. As such, timely payment depends on the municipality’s ability to raise tax revenue and maintain a fiscally sound budget. The timely payments may also be influenced by any unfunded pension liabilities or other post-employee benefit plan (OPEB) liabilities.

Revenue bonds are secured by special tax revenues or other revenue sources. If the specified revenues do not materialize, then the bonds may not be repaid.

Private activity bonds are yet another type of municipal security. Municipalities use private activity bonds to finance the development of industrial facilities for use by private enterprise. Principal and interest payments are to be made by the private enterprise benefitting from the development, which means that the holder of the bond is exposed to the risk that the private issuer may default on the bond.

Moral obligation bonds are usually issued by special purpose public entities. If the public entity defaults, repayment becomes a “moral obligation” instead of a legal one. The lack of a legally enforceable right to payment in the event of default poses a special risk for a holder of the bond because it has little or no ability to seek recourse in the event of default.

In addition, a significant restructuring of federal income tax rates or even serious discussion on the topic in Congress could cause municipal bond prices to fall. The demand for municipal securities is strongly influenced by the value of tax-exempt income to investors. Lower income tax rates could reduce the advantage of owning municipal securities.

Municipal notes are similar to general municipal debt obligations, but they generally possess shorter terms. Municipal notes can be used to provide interim financing and may not be repaid if anticipated revenues are not realized.

Municipal Project-Specific Risk

The Fund may be more sensitive to adverse economic, business or political developments if it invests a substantial portion of its assets in the bonds of specific projects (such as those relating to education, health care, housing, transportation, and utilities), industrial development bonds, or in general obligation bonds, particularly if there is a large concentration from issuers in a single state. This is because the value of municipal securities can be significantly affected by the political, economic, legal, and legislative realities of the particular issuer’s locality or municipal sector events. Similarly, changes to state or federal regulation tied to a specific sector, such as the hospital sector, could have an impact on the revenue stream for a given subset of the market.

U.S. Government Securities Risk

Certain U.S. government securities, such as U.S. Treasury bills, notes, bonds, and mortgage-related securities guaranteed by the Government National Mortgage Association (“GNMA”), are supported by the full faith and credit of the United States; others, such as those of the Federal Home Loan Banks (“FHLBs”) or the Federal Home Loan Mortgage Corporation (“FHLMC”), are supported by the right of the issuer to borrow from the U.S. Treasury; others, such as those of the Federal National Mortgage Association (“FNMA”), are supported by the discretionary authority of the U.S. government to purchase the agency’s obligations; and still others are supported only by the credit of the agency, instrumentality or corporation. Although legislation has been

[ ] | Base Prospectus 6

PIMCO Municipal Income Fund

enacted to support certain government sponsored entities, including the FHLBs, FHLMC and FNMA, there is no assurance that the obligations of such entities will be satisfied in full, or that such obligations will not decrease in value or default. It is difficult, if not impossible, to predict the future political, regulatory or economic changes that could impact the government sponsored entities and the values of their related securities or obligations. In addition, certain governmental entities, including FNMA and FHLMC, have been subject to regulatory scrutiny regarding their accounting policies and practices and other concerns that may result in legislation, changes in regulatory oversight and/or other consequences that could adversely affect the credit quality, availability or investment character of securities issued by these entities. Yields available from U.S. government debt securities are generally lower than the yields available from other debt securities. The values of U.S. government securities change as interest rates fluctuate.

California State-Specific Risk

The Fund may be affected significantly by economic, regulatory or political developments affecting the ability of California issuers to pay interest or repay principal. Certain issuers of California municipal bonds have experienced serious financial difficulties in the past and reoccurrence of these difficulties may impair the ability of certain California issuers to pay principal or interest on their obligations. Provisions of the California Constitution and State statutes which limit the taxing and spending authority of California governmental entities may impair the ability of California issuers to pay principal and/or interest on their obligations. While California’s economy is broad, it does have major concentrations in advanced technology, aerospace and defense-related manufacturing, trade, entertainment, real estate and financial services, and may be sensitive to economic problems affecting those industries. Future California political and economic developments, constitutional amendments, legislative measures, executive orders, administrative regulations, litigation and voter initiatives could have an adverse effect on the debt obligations of California issuers.

New York State-Specific Risk. The Fund may be affected significantly by economic, regulatory or political developments affecting the ability of New York issuers to pay interest or repay principal. Certain issuers of New York municipal bonds have experienced serious financial difficulties in the past and reoccurrence of these difficulties may impair the ability of certain New York issuers to pay principal or interest on their obligations. Provisions of the New York Constitution and State statutes which limit the taxing and spending authority of New York governmental entities may impair the ability of New York issuers to pay principal and/or interest on their obligations. While New York’s economy is broad, it does have major concentrations in certain industries, such as financial services, and may be sensitive to economic problems affecting those industries. Future New York political and economic developments, constitutional amendments, legislative measures, executive orders, administrative regulations, litigation and voter initiatives could have an adverse effect on the debt obligations of New York issuers.

Puerto Rico-Specific Risk

The Fund may be affected significantly by economic, regulatory, restructuring or political developments affecting the ability of Puerto Rico issuers to pay interest or repay principal. Certain issuers of Puerto Rico municipal bonds have experienced serious financial difficulties in the past and reoccurrence of these difficulties may impair the ability of certain Puerto Rico issuers to pay principal or interest on their obligations. Provisions of the Puerto Rico Constitution and Commonwealth laws, including a federally-appointed oversight board to oversee the Commonwealth’s financial operations, which limit the taxing and spending authority of Puerto Rico governmental entities may impair the ability of Puerto Rico issuers to pay principal and/or interest on their obligations. While Puerto Rico’s economy is broad, it does have major concentrations in certain industries, such as manufacturing and service, and may be sensitive to economic problems affecting those industries. Future Puerto Rico political and economic developments, constitutional amendments, legislative measures, executive orders, administrative regulations, litigation, debt restructuring, and voter initiatives could have an adverse effect on the debt obligations of Puerto Rico issuers.

Asset Allocation Risk

The Fund’s investment performance depends upon how its assets are allocated and reallocated. A principal risk of investing in the Fund is that PIMCO may make less than optimal or poor asset allocation decisions. PIMCO employs an active approach to allocation among multiple fixed- income sectors, but there is no guarantee that such allocation techniques will produce the desired results. It is possible that PIMCO will focus on an investment that performs poorly or underperforms other investments under various market conditions. You could lose money on your investment in the Fund as a result of these allocation decisions.

Management Risk

The Fund is subject to management risk because it is an actively managed investment portfolio. PIMCO and each individual portfolio manager will apply investment techniques and risk analysis in making investment decisions for the Fund, but there can be no guarantee that these decisions will produce the desired results. Certain securities or other instruments in which the Fund seeks to invest may not be available in the quantities desired. In addition, regulatory restrictions, actual or potential conflicts of interest or other considerations may cause PIMCO to restrict or prohibit participation in certain investments. In such circumstances, PIMCO or the individual portfolio managers may determine to purchase other securities or instruments as substitutes. Such substitute securities or instruments may not perform as intended, which could result in losses to the Fund. The Fund is also subject to the risk that deficiencies in the internal systems or controls of PIMCO or another service provider will cause losses for the Fund or hinder Fund operations. For example, trading delays or errors (both human and systemic) could prevent the Fund from purchasing a security expected to appreciate in value. To the extent the Fund employs strategies targeting perceived pricing inefficiencies, arbitrage strategies or similar strategies, it is subject to the risk that the pricing or valuation of the securities and

7 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

instruments involved in such strategies may change unexpectedly, which may result in reduced returns or losses to the Fund. Additionally, actual or potential conflicts of interest, legislative, regulatory, or tax restrictions, policies or developments may affect the investment techniques available to PIMCO and each individual portfolio manager in connection with managing the Fund and may also adversely affect the ability of the Fund to achieve its investment objectives. There also can be no assurance that all of the personnel of PIMCO will continue to be associated with PIMCO for any length of time. The loss of the services of one or more key employees of PIMCO could have an adverse impact on the Fund’s ability to realize its investment objectives.

In addition, the Fund may rely on various third-party sources to calculate its NAV. As a result, the Fund is subject to certain operational risks associated with reliance on service providers and service providers’ data sources. In particular, errors or systems failures and other technological issues may adversely impact the Fund’s calculations of its NAV, and such NAV calculation issues may result in inaccurately calculated NAVs, delays in NAV calculation and/or the inability to calculate NAV over extended periods. The Fund may be unable to recover any losses associated with such failures.

Issuer Risk

The value of a security may decline for a number of reasons that directly relate to the issuer, such as management performance, financial leverage and reduced demand for the issuer’s goods or services, as well as the historical and prospective earnings of the issuer and the value of its assets. A change in the financial condition of a single issuer may affect securities markets as a whole. These risks can apply to the Common Shares issued by the Fund and to the issuers of securities and other instruments in which the Fund invests.

Interest Rate Risk

Interest rate risk is the risk that fixed income securities and other instruments in the Fund’s portfolio will decline in value because of a change in interest rates. Interest rate changes can be sudden and unpredictable, and the Fund may lose money as a result of movements in interest rates.

A wide variety of factors can cause interest rates or yields of U.S. Treasury securities (or yields of other types of bonds) to rise (e.g., central bank monetary policies, inflation rates, general economic conditions). Recently, there have been signs of inflationary price movements. As such, fixed income securities markets may experience heightened levels of interest rate, volatility and liquidity risk.

Rising interest rates may result in periods of volatility and a decline in value of the Fund’s fixed income investments.

Credit Risk

of the credit of a security held by the Fund may decrease its value. Measures such as average credit quality may not accurately reflect the true credit risk of the Fund. This is especially the case if the Fund consists of securities with widely varying credit ratings. This risk is greater to the extent the Fund uses leverage or derivatives. Municipal bonds are subject to the risk that litigation, legislation or other political events, local business or economic conditions, or the bankruptcy of the issuer could have a significant effect on an issuer’s ability to make payments of principal and/or interest.

Mortgage-Related and Other Asset-Backed Instruments Risk

The Fund may also invest in the residual or equity tranches of mortgage-related and other asset-backed instruments, which may be referred to as subordinate mortgage-backed or asset-backed instruments and interest-only mortgage-backed or asset-backed instruments. The Fund expects that investments in subordinate mortgage-backed and other asset-backed instruments will be subject to risks arising from delinquencies and foreclosures, thereby exposing its investment portfolio to potential losses. Subordinate securities of mortgage-backed and other asset-backed instruments are also subject to greater credit risk than those mortgage-backed or other asset-backed instruments that are more highly rated.

The mortgage markets in the United States and in various foreign countries have experienced extreme difficulties in the past that adversely affected the performance and market value of certain mortgage-related investments. Delinquencies and losses on residential and commercial mortgage loans (especially subprime and second-lien mortgage loans) may increase, and a decline in or flattening of housing and other real property values may exacerbate such delinquencies and losses. In addition, reduced investor demand for mortgage loans and mortgage-related securities and increased investor yield requirements have caused limited liquidity in the secondary market for mortgage-related securities, which can adversely affect the market value of mortgage-related securities. It is possible that such limited liquidity in such secondary markets could continue or worsen.

[ ] | Base Prospectus 8

PIMCO Municipal Income Fund

Mortgage-Related Derivative Instruments Risk

Mortgage-related derivative instruments involve risks associated with mortgage-related and other asset-backed instruments, privately-issued mortgage-related securities, the mortgage market, the real estate industry, derivatives and credit default swaps. See “Mortgage-Related and Other Asset-Backed Instruments Risk,” “Privately-Issued Mortgage-Related Securities Risk,” “Derivatives Risk,” and “Credit Default Swaps Risk.”

High Yield Securities Risk

To the extent that the Fund invests in high yield securities and unrated securities of similar credit quality (commonly known as “high yield securities” or “junk bonds”), the Fund will be subject to greater levels of credit risk, call risk and liquidity risk than funds that do not invest in such securities, which could have a negative effect on the NAV and market price of the Fund’s Common Shares or Common Share dividends. These securities are considered predominantly speculative with respect to an issuer’s continuing ability to make principal and interest payments, and may be more volatile than other types of securities. An economic downturn or individual corporate developments could adversely affect the market for these securities and reduce the Fund’s ability to sell these securities at an advantageous time or price. The Fund may purchase distressed securities that are in default or the issuers of which are in bankruptcy, which involve heightened risks.

In general, lower rated debt securities carry a greater degree of risk that the issuer will lose its ability to make interest and principal payments, which could have a negative effect on the NAV and market price of the Fund’s Common Shares or Common Share dividends. Securities of below investment grade quality are regarded as having predominantly speculative characteristics with respect to capacity to pay interest and repay principal, and are commonly referred to as “high yield” securities or “junk bonds.” High yield securities involve a greater risk of default and their prices are generally more volatile and sensitive to actual or perceived negative developments.

An economic downturn could severely affect the ability of issuers (particularly those that are highly leveraged) to service or repay their debt obligations. The Fund may purchase stressed or distressed securities that are in default or the issuers of which are in bankruptcy, which involve heightened risks. Lower-rated securities are generally less liquid than higher-rated securities, which may have an adverse effect on the Fund’s ability to dispose of a particular security. To the extent the Fund focuses on below investment grade debt obligations, PIMCO’s capabilities in analyzing credit quality and associated risks will be particularly important, and there can be no assurance that PIMCO will be successful in this regard. Due to the risks involved in investing in high yield securities, an investment in the Fund should be considered speculative.

credit characteristics of a particular issue. Analysis of creditworthiness may be more complex for issuers of high yield securities than for issuers of higher quality debt securities.

Call Risk

Call risk refers to the possibility that an issuer may exercise its right to redeem a fixed income security earlier than expected. Issuers may call outstanding securities prior to their maturity for a number of reasons. If an issuer calls a security in which the Fund has invested, the Fund may not recoup the full amount of its initial investment and may be forced to reinvest in lower-yielding securities, securities with greater credit risks or securities with other, less favorable features.

Reinvestment Risk

Income from the Fund’s portfolio will decline if and when the Fund invests the proceeds from matured, traded or called debt obligations at market interest rates that are below the portfolio’s current earnings rate. For instance, during periods of declining interest rates, an issuer of debt obligations may exercise an option to redeem securities prior to maturity, forcing the Fund to invest in lower-yielding securities. The Fund also may choose to sell higher yielding portfolio securities and to purchase lower yielding securities to achieve greater portfolio diversification, because the portfolio managers believe the current holdings are overvalued or for other investment-related reasons. A decline in income received by the Fund from its investments is likely to have a negative effect on dividend levels and the market price, NAV and/or overall return of the Common Shares.

Securities Lending Risk

For the purpose of achieving income, the Fund may lend its portfolio securities to brokers, dealers, and other financial institutions provided a number of conditions are satisfied, including that the loan is fully collateralized. Please see “Investment Objectives and Policies—Loans of Portfolio Securities” in the Statement of Additional Information for more details. When the Fund lends portfolio securities, its investment performance will continue to reflect changes in the value of the securities loaned, and the Fund will also receive a fee or interest on the collateral. Securities lending involves the risk of loss of rights in the collateral or delay in recovery of the collateral if the borrower fails to return the security loaned or becomes insolvent. The Fund may pay lending fees to a party arranging the loan. Cash collateral received by the Fund in securities lending transactions may be invested in short-term liquid fixed income instruments or in money market or short-term mutual funds, or similar investment vehicles, including affiliated money market or short-term mutual funds. The Fund bears the risk of such investments.

Valuation Risk

9 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

Fair value pricing may require subjective determinations about the value of a security or other asset. As a result, there can be no assurance that fair value pricing will result in adjustments to the prices of securities or other assets or that fair value pricing will reflect actual market value, and it is possible that the fair value determined for a security or other asset will be materially different from quoted or published prices, from the prices used by others for the same security or other asset and/or from the value that actually could be or is realized upon the sale of that security or other asset.

Leverage Risk

The Fund’s use of leverage (as described under “Use of Leverage” in the body of this prospectus) creates the opportunity for increased Common Share net income, but also creates special risks for Common Shareholders. To the extent used, there is no assurance that the Fund’s leveraging strategies will be successful. Leverage is a speculative technique that may expose the Fund to greater risk and increased costs. The Fund’s assets attributable to any outstanding Preferred Shares (such as the ARPS and RVMTP Shares) or the net proceeds that the Fund obtains from its use of TOBs, derivatives or other forms of leverage, if any, will be invested in accordance with the Fund’s investment objective and policies as described in this prospectus. Dividends payable with respect to Preferred Shares outstanding and interest expense payable by the Fund with respect to any TOBs, derivatives and other forms of leverage will generally be based on shorter-term interest rates that would be periodically reset. If shorter-term interest rates rise relative to the rate of return on the Fund’s portfolio, the interest and other costs to the Fund of leverage (including interest expenses on TOBs and the dividend rate on any outstanding Preferred Shares, including the Preferred Shareholder Gross-Up (as defined below)) could exceed the rate of return on the debt obligations and other investments held by the Fund, thereby reducing return to Common Shareholders. In addition, fees and expenses of any form of leverage used by the Fund will be borne entirely by the Common Shareholders (and not by preferred shareholders) and will reduce the investment return of the Common Shares. Therefore, there can be no assurance that the Fund’s use of leverage will result in a higher yield on the Common Shares, and it may result in losses. In addition, Preferred Shares issued by the Fund pay cumulative dividends, which may tend to increase leverage risk. Leverage creates several major types of risks for Common Shareholders, including:

◾

the likelihood of greater volatility of NAV and market price of Common Shares, and of the investment return to Common Shareholders, than a comparable portfolio without leverage;

◾

the possibility either that Common Share dividends will fall if the interest and other costs of leverage rise, or that dividends paid on Common Shares will fluctuate because such costs vary over time; and

◾

the effects of leverage in a declining market or a rising interest rate environment, as leverage is likely to cause a greater decline in the NAV of the Common Shares than if the Fund were not leveraged and may result in a greater decline in the market value of the Common Shares.

In addition, the counterparties to the Fund’s leveraging transactions and preferred shareholders of the Fund will have priority of payment over the Fund’s Common Shareholders.

The Fund is required to satisfy certain asset coverage requirements in connection with its use of Preferred Shares, including those imposed by regulatory and rating agency requirements. Accordingly, any decline in the net asset value of the Fund’s investments could result in the risk that the Fund will fail to meet its asset coverage requirements for Preferred Shares or the risk of the Preferred Shares being downgraded by a rating agency. In an extreme case, the Fund’s current investment income might not be sufficient to meet the dividend requirements on Preferred Shares outstanding. In order to address these types of events, the Fund might need to dispose of investments in order to fund a redemption of some or all of the Preferred Shares. Dispositions at times of adverse economic conditions may result in a loss to the Fund. At other times, these dispositions may result in gain at the Fund level and thus in additional taxable distributions to Common Shareholders. See “Tax Matters” for more information. Any Preferred Shares, TOBs, loans of portfolio securities, short sales and when-issued, delayed delivery and forward commitment transactions, credit default swaps, reverse repurchases, or other derivatives by the Fund or counterparties to the Fund’s other leveraging transactions, if any, would have, seniority over the Fund’s Common Shares.

When the Fund issues Preferred Shares, the Fund pays (and the Common Shareholders bear) all costs and expenses relating to the issuance and ongoing maintenance of Preferred Shares. In addition, holders of Preferred Shares issued by the Fund would have complete priority over Common Shareholders in the distribution of the Fund’s assets. Furthermore, preferred shareholders, voting separately as a single class, have the right to elect two members of the Board at all times and to elect a majority of the trustees in the event two full years’ dividends on the Preferred Shares are unpaid, and also have separate class voting rights on certain matters. Accordingly, preferred shareholders may have interests that differ from those of Common Shareholders, and may at times have disproportionate influence over the Fund’s affairs.

Because the fees received by the Investment Manager are based on the average daily net asset value of the Fund (including daily net assets attributable to any Preferred Shares), the Investment Manager has a financial incentive for the Fund to utilize Preferred Shares, which may create a conflict of interest between the Investment Manager, on the one hand, and the Common Shareholders, on the other hand.

Derivatives Risk

The use of derivative instruments involves risks different from, and possibly greater than, the risks associated with investing directly in securities and other traditional investments. Derivatives are subject to a number of risks, such as liquidity risk, interest rate risk, market risk, credit risk, leveraging risk, counterparty risk, tax risk, and management risk, as well as risks arising from changes in applicable requirements.

[ ] | Base Prospectus 10

PIMCO Municipal Income Fund

They also involve the risk of mispricing, the risk of unfavorable or ambiguous documentation and the risk that changes in the value of a derivative may not correlate perfectly with the underlying asset, rate or index.

The Fund’s use of derivatives may increase or accelerate the amount of taxes payable by Common Shareholders.

The regulation of the derivatives markets has increased over the past several years, and additional future regulation of the derivatives markets may make derivatives more costly, may limit the availability or reduce the liquidity of derivatives or may otherwise adversely affect the value or performance of derivatives.

Credit Default Swaps Risk

Credit default swap agreements may involve greater risks than if the Fund had invested in the reference obligation directly since, in addition to general market risks, credit default swaps are subject to illiquidity risk, counterparty risk and credit risk. A buyer generally also will lose its investment and recover nothing should no credit event occur and the swap is held to its termination date. If a credit event were to occur, the value of any deliverable obligation received by the seller (if any), coupled with the upfront or periodic payments previously received, may be less than the full notional value it pays to the buyer, resulting in a loss of value to the seller. When the Fund acts as a seller of a credit default swap, it is exposed to many of the same risks of leverage described herein since if an event of default occurs, the seller must pay the buyer the full notional value of the reference obligation.

Although the Fund may seek to realize gains by selling credit default swaps that increase in value, to realize gains on selling credit default swaps, an active secondary market for such instruments must exist or the Fund must otherwise be able to close out these transactions at advantageous times. In addition to the risk of losses described above, if no such secondary market exists or the Fund is otherwise unable to close out these transactions at advantageous times, selling credit default swaps may not be profitable for the Fund.

The market for credit default swaps has become more volatile as the creditworthiness of certain counterparties has been questioned and/or downgraded. The Fund will be subject to credit risk with respect to the counterparties to the credit default swap contract (whether a clearing corporation or another third party). If a counterparty’s credit becomes significantly impaired, multiple requests for collateral posting in a short period of time could increase the risk that the Fund may not receive adequate collateral. The Fund may exit its obligations under a credit default swap only by terminating the contract and paying applicable breakage fees, or by entering into an offsetting credit default swap position, which may cause the Fund to incur more losses.

Counterparty Risk

the subject of a bankruptcy case, the derivative transaction may be terminated in accordance with its terms and the Fund’s ability to realize its rights under the derivative instrument and its ability to distribute the proceeds could be adversely affected. If a counterparty becomes bankrupt or otherwise fails to perform its obligations under a derivative contract due to financial difficulties, the Fund may experience significant delays in obtaining any recovery (including recovery of any collateral it has provided to the counterparty) in a dissolution, assignment for the benefit of creditors, liquidation, winding-up, bankruptcy or other analogous proceeding. In addition, in the event of the insolvency of a counterparty to a derivative transaction, the derivative transaction would typically be terminated at its fair market value. If the Fund is owed this fair market value in the termination of the derivative transaction and its claim is unsecured, the Fund will be treated as a general creditor of such counterparty and will not have any claim with respect to any underlying security or asset. The Fund may obtain only a limited recovery or may obtain no recovery in such circumstances. While the Fund may seek to manage its counterparty risk by transacting with a number of counterparties, concerns about the solvency of, or a default by, one large market participant could lead to significant impairment of liquidity and other adverse consequences for other counterparties.

Additional Risks Associated with the Fund’s Preferred Shares

Although the Fund’s ARPS ordinarily would pay dividends at rates set at periodic auctions, the weekly auctions for the ARPS (and auctions for similar preferred shares issued by closed-end funds in the U.S.) have failed since 2008. The dividend rates on the ARPS since that time have been paid, and the Fund expects that it will continue to be paid for the foreseeable future, at the “maximum applicable rate.”

The maximum applicable rate for the ARPS and the RVMTP Share Dividend Rate (as defined below) is based in part on a multiple of or a spread plus a reference rate. An increase in market interest rates generally, therefore, could increase substantially the dividend rate required to be paid by the Fund to the holders of Preferred Shares, which would increase the costs associated with the Fund’s leverage and reduce the Fund’s net income available for distribution to holders of Common Shares. In addition, the multiple or spread used to calculate the maximum applicable rate for the ARPS and the RVMTP Share Dividend Rate is based in part on the credit rating assigned to the ARPS or RVMTP Shares by the applicable rating agency(ies), with the multiple or spread generally increasing as the rating declines. Accordingly, future ratings downgrades may result in increases to the maximum applicable rate for the ARPS or to the RVMTP Share Dividend Rate.

Therefore, it is possible that a substantial rise in market interest rates and/or further ratings downgrades of the Preferred Shares could, by reducing income available for distribution to the holders of Common Shares and otherwise detracting from the Fund’s investment performance, make the Fund’s continued use of Preferred Shares for leverage purposes less attractive than such use is currently considered to be. In such case, the Fund may elect to redeem some or all of the Preferred Shares outstanding, which may require it to dispose of investments at inopportune times and to incur losses on such

11 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

dispositions. Such dispositions may adversely affect the Fund’s investment performance generally, and the resultant loss of leverage may materially and adversely affect the Fund’s investment returns.

The Fund is also subject to certain asset coverage tests associated with the rating agencies that rate the Preferred Shares. Failure by the Fund to maintain the asset coverages (or to cure such failure in a timely manner) may require the Fund to redeem Preferred Shares and could preclude the Fund from declaring or paying any dividends or distributions to holders of Common Shares. Failure to satisfy ratings agency asset coverage tests or other guidelines could also result in the applicable ratings agency downgrading its then-current ratings on the Preferred Shares, as described above. Moreover, the rating agency guidelines impose restrictions or limitations on the Fund’s use of certain financial instruments or investment techniques that the Fund might otherwise utilize in order to achieve its investment objective, which may adversely affect the Fund’s investment performance. Rating agency guidelines may be modified by the rating agencies in the future and such modifications may make such guidelines substantially more restrictive or otherwise result in downgrades, which could further negatively affect the Fund’s investment performance.

The ratings agencies that have assigned ratings to the Fund’s Preferred Shares may change their rating methodologies, perhaps substantially. Such a change could adversely affect the ratings assigned to the Fund’s Preferred Shares, the dividend rates paid thereon, and the expenses borne by holders of Common Shares. For instance, Fitch Ratings published ratings criteria relating to closed-end funds on December 4, 2020, which effectively result in a rating cap of “AA” for debt and preferred stock issued by all closed-end funds and a rating cap of “A” for debt and preferred shares issued by (i) closed-end funds exposed to emerging market debt, below-investment-grade and unrated debt, structured securities and equity, and (ii) closed-end funds with material exposure to “BBB” category rated assets. On December 6, 2021, Fitch affirmed “AA” long-term ratings of the Fund’s RVMTP Shares. Fitch does not currently rate the Fund’s ARPS. In addition, future ratings downgrades by Moody’s or Fitch, as applicable, may result in an increase to the Fund’s Preferred Shares dividend rates.

Private Placements and Restricted Securities Risk

A private placement involves the sale of securities that have not been registered under the Securities Act or relevant provisions of applicable non-U.S. law to certain institutional and qualified individual purchasers, such as the Fund. In addition to the general risks to which all securities are subject, securities received in a private placement generally are subject to strict restrictions on resale, and there may be no liquid secondary market or ready purchaser for such securities. Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most favorable time or price. Private placements may also raise valuation risks. Restricted securities are often purchased at a discount from the market price of unrestricted securities of the same issuer reflecting the fact that such securities may not be readily marketable without some time delay. Such securities are often more difficult to value and the sale of such securities often requires more time and results in higher brokerage charges or dealer discounts and other

selling expenses than does the sale of securities trading on national securities exchanges or in the over-the-counter markets. Until the Fund can sell such securities into the public markets, its holdings may be less liquid and any sales will need to be made pursuant to an exemption under the Securities Act.

Confidential Information Access Risk

In managing the Fund (and other PIMCO clients), PIMCO may from time to time have the opportunity to receive material, non-public information (“Confidential Information”) about the issuers of certain investments, including, without limitation, senior floating rate loans, other loans and related investments being considered for acquisition by the Fund or held in the Fund’s portfolio. For example, an issuer of privately placed loans considered by the Fund may offer to provide PIMCO with financial information and related documentation regarding the issuer that is not publicly available. Pursuant to applicable policies and procedures, PIMCO may (but is not required to) seek to avoid receipt of Confidential Information from the issuer so as to avoid possible restrictions on its ability to purchase and sell investments on behalf of the Fund and other clients to which such Confidential Information relates. In such circumstances, the Fund (and other PIMCO clients) may be disadvantaged in comparison to other investors, including with respect to the price the Fund pays or receives when it buys or sells an investment. Further, PIMCO’s and the Fund’s abilities to assess the desirability of proposed consents, waivers or amendments with respect to certain investments may be compromised if they are not privy to available Confidential Information. PIMCO may also determine to receive such Confidential Information in certain circumstances under its applicable policies and procedures. If PIMCO intentionally or unintentionally comes into possession of Confidential Information, it may be unable, potentially for a substantial period of time, to purchase or sell investments to which such Confidential Information relates.

Inflation/Deflation Risk

Inflation risk is the risk that the value of assets or income from the Fund’s investments will be worth less in the future as inflation decreases the value of payments at future dates. As inflation increases, the real value of the Fund’s portfolio could decline. Inflation has recently increased and it cannot be predicted whether it may decline. Deflation risk is the risk that prices throughout the economy decline over time. Deflation may have an adverse effect on the creditworthiness of issuers and may make issuer default more likely, which may result in a decline in the value of the Fund’s portfolio and Common Shares.

Regulatory Changes Risk

[ ] | Base Prospectus 12

PIMCO Municipal Income Fund

been eligible for exemptions from certain regulations. However, there is no assurance that the Fund and the Investment Manager will continue to be eligible for such exemptions. Actions by government entities may also impact certain instruments in which the Fund invests.

Moreover, government regulation may have unpredictable and unintended effects. Legislative or regulatory actions to address perceived liquidity or other issues in fixed income markets generally, or in particular markets such as the municipal securities market, may alter or impair the Fund’s ability to pursue its investment objectives or utilize certain investment strategies and techniques.

Current rules related to credit risk retention requirements for ABS may increase the cost to originators, securitizers and, in certain cases, asset managers of SPEs in which the Fund may invest. The impact of the risk retention rules on the securitization markets is uncertain. These requirements may increase the costs to originators, securitizers, and, in certain cases, collateral managers of securitization vehicles in which the Fund may invest, which costs could be passed along to the Fund as an investor in such vehicles. In addition, the costs imposed by the risk retention rules on originators, securitizers and/or collateral managers may result in a reduction of the number of new offerings of ABS and thus in fewer investment opportunities for the Fund. A reduction in the number of new securitizations could also reduce liquidity in the markets for certain types of financial assets, which in turn could negatively affect the returns on the Fund’s investment.

Regulatory Risk—London Interbank Offered Rate (“LIBOR”)

increasingly well-defined in advance of the anticipated discontinuation date, there remains uncertainty regarding the future utilization of LIBOR and the nature of any replacement rate (e.g., the Secured Overnight Financing Rate, which is intended to replace U.S. dollar LIBOR and measures the cost of overnight borrowings through repurchase agreement transactions collateralized with U.S. Treasury securities). Any potential effects of the transition away from LIBOR on the Fund or on certain instruments in which the Fund invests can be difficult to ascertain, and they may vary depending on factors that include, but are not limited to: (i) existing fallback or termination provisions in individual contracts and (ii) whether, how, and when industry participants develop and adopt new reference rates and fallbacks for both legacy and new products and instruments. For example, certain of the Fund’s investments may involve individual contracts that have no existing fallback provision or language that contemplates the discontinuation of LIBOR, and those investments could experience increased volatility or illiquidity as a result of the transition process. In addition, interest rate provisions included in such contracts, or in contracts or other arrangements entered into by the Fund, may need to be renegotiated. On March 15, 2022, the Adjustable Interest Rate (LIBOR) Act was signed into law. This law provides a statutory fallback mechanism on a nationwide basis to replace LIBOR with a benchmark rate that is selected by the Board of Governors of the Federal Reserve System and based on the Secured Overnight Financing Rate for certain contracts that reference LIBOR and contain no, or insufficient, fallback provisions. It is expected that implementing regulations in respect of the law will follow. The transition of investments from LIBOR to a replacement rate as a result of amendment, application of existing fallbacks, statutory requirements or otherwise may also result in a reduction in the value of certain instruments held by the Fund, a change in the cost of borrowing or the dividend rate for any Preferred Shares that may be issued by the Fund, or a reduction in the effectiveness of related Fund transactions such as hedges. Any such effects of the transition away from LIBOR, as well as other unforeseen effects, could result in losses to the Fund.

Regulatory Risk—Commodity Pool Operator

The CFTC has adopted regulations that subject registered investment companies and their investment advisers to regulation by the CFTC if the registered investment company invests more than a prescribed level of its liquidation value in futures, options on futures or commodities, swaps, or other financial instruments regulated under the Commodity Exchange Act (“CEA”) and the rules thereunder (“commodity interests”), or if the Fund markets itself as providing investment exposure to such instruments. The Investment Manager is registered with the CFTC as a CPO. However, with respect to the Fund, the Investment Manager has claimed an exclusion from registration as a CPO pursuant to CFTC Rule 4.5. For the Investment Manager to remain eligible for this exclusion, the Fund must comply with certain limitations, including limits on its ability to use any commodity interests and limits on the manner in which the Fund holds out its use of such commodity interests. These limitations may restrict the Fund’s ability to pursue its investment objectives and strategies, increase the costs of implementing its strategies, result in higher expenses for the Fund, and/or adversely

13 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

affect the Fund’s total return. To the extent the Fund becomes ineligible for this exclusion from CFTC regulation, the Fund may consider steps in order to continue to qualify for exemption from CFTC regulation, or may determine to operate subject to CFTC regulation.

Liquidity Risk. Liquidity risk exists when particular investments are difficult to purchase or sell. Illiquid investments are investments that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. Illiquid investments may become harder to value, especially in changing markets. The Fund’s investments in illiquid investments may reduce the returns of the Fund because it may be unable to sell the illiquid investments at an advantageous time or price or possibly require the Fund to dispose of other investments at unfavorable times or prices in order to satisfy its obligations, which could prevent the Fund from taking advantage of other investment opportunities. Additionally, the market for certain investments may become illiquid under adverse market or economic conditions independent of any specific adverse changes in the conditions of a particular issuer. To the extent that the Fund invests in securities of companies with smaller market capitalizations, foreign (non-U.S.) securities, Rule 144A securities, illiquid sectors of fixed income securities, derivatives or securities with substantial market and/or credit risk, the Fund will tend to have greater exposure to liquidity risk.

Further fixed income securities with longer durations until maturity face heightened levels of liquidity risk as compared to fixed income securities with shorter durations until maturity. The risks associated with illiquid instruments may be particularly acute in situations in which the Fund’s operations require cash (such as in connection with tender offers) and could result in the Fund borrowing to meet its short-term needs or incurring losses on the sale of illiquid instruments. It may also be the case that other market participants may be attempting to liquidate fixed income holdings at the same time as the Fund, causing increased supply in the market and contributing to liquidity risk and downward pricing pressure.

To the extent the Fund invests in Alt Lending ABS, the Alt Lending ABS in which the Fund invests are typically not listed on any securities exchange and not registered under the Securities Act. In addition, the Fund anticipates that these instruments may only be sold to a limited number of investors and may have a limited or non-existent secondary market. Accordingly, the Fund currently expects that certain of its investments in Alt Lending ABS will face heightened levels of liquidity risk. Although currently, there is generally no active reliable, secondary market for certain Alt Lending ABS, a secondary market for these alternative lending-related instruments may develop.

Tax Risk

The Fund has elected to be treated as a “regulated investment company” (a “RIC”) under the Code and intends each year to qualify and be eligible to be treated as such, so that it generally will not be subject to U.S. federal income tax on its net investment income or net short-term or long-term capital gains, that are distributed to

shareholders. In order to qualify and be eligible for such treatment, the Fund must meet certain asset diversification tests, derive at least 90% of its gross income for such year from certain types of qualifying income, and distribute to its shareholders at least 90% of its “investment company taxable income” as that term is defined in the Code (which includes, among other things, dividends, taxable interest and the excess of any net short-term capital gains over net long-term capital losses, as reduced by certain deductible expenses).

The Fund’s investment strategy will potentially be limited by its intention to continue qualifying for treatment as a RIC, and can limit the Fund’s ability to continue qualifying as such. The tax treatment of certain of the Fund’s investments under one or more of the qualification or distribution tests applicable to RICs is uncertain. An adverse determination or future guidance by the Internal Revenue Service (“IRS”) or a change in law might affect the Fund’s ability to qualify or be eligible for treatment as a RIC. Income and gains from certain of the Fund’s activities may not constitute qualifying income to a RIC for purposes of the 90% gross income test. If the Fund were to treat income or gain from a particular investment or activity as qualifying income and the income or gain were later determined not to constitute qualifying income and, together with any other nonqualifying income, caused the Fund’s nonqualifying income to exceed 10% of its gross income in any taxable year, the Fund would fail to qualify as a RIC unless it is eligible to and does pay a tax at the Fund level.

If, in any year, the Fund were to fail to qualify for treatment as a RIC under the Code, and was ineligible to or did not otherwise cure such failure, the Fund would be subject to tax on its taxable income at corporate rates and, when such income is distributed, shareholders would be subject to further tax on such distributions to the extent of the Fund’s current or accumulated earnings and profits.

Portfolio Turnover Risk

The Investment Manager manages the Fund without regard generally to restrictions on portfolio turnover. The use of futures contracts and other derivative instruments with relatively short maturities may tend to exaggerate the portfolio turnover rate for the Fund. Trading in fixed income securities does not generally involve the payment of brokerage commissions but does involve indirect transaction costs. The use of futures contracts and other derivative instruments may involve the payment of commissions to futures commission merchants or other intermediaries. Higher portfolio turnover involves correspondingly greater expenses to the Fund, including brokerage commissions or dealer mark-ups and other transaction costs on the sale of securities and reinvestments in other securities. The higher the rate of portfolio turnover of the Fund, the higher these transaction costs borne by the Fund generally will be. Such sales may result in realization of taxable capital gains (including short-term capital gains, which are generally taxed to shareholders at ordinary income tax rates when distributed net of short-term capital losses and net long-term capital losses), and may adversely impact the Fund’s after-tax returns.

[ ] | Base Prospectus 14

PIMCO Municipal Income Fund

Operational Risk

An investment in the Fund, like any fund, involves operational risks arising from factors such as processing errors, human errors, inadequate or failed internal or external processes, failures in systems and technology, changes in personnel and errors caused by third-party service providers. The occurrence of any of these failures, errors or breaches could result in a loss of information, regulatory scrutiny, reputational damage or other events, any of which could have a material adverse effect on the Fund. While the Fund seeks to minimize such events through controls and oversight, there may still be failures that could cause losses to the Fund.

Other Investment Companies Risk

When investing in an investment company, the Fund generally will bear its ratable share of that investment company’s expenses and remain subject to payment of the Fund’s management fees and other expenses with respect to assets so invested. Common Shareholders could therefore be subject to duplicative expenses to the extent the Fund invests in other investment companies. In addition, the securities of other investment companies may also be leveraged and will therefore be subject to the same leverage risks.

Cybersecurity Risk

As the use of technology has become more prevalent in the course of business, the Fund is potentially more susceptible to operational and information security risks resulting from breaches in cyber security. A breach in cyber security refers to both intentional and unintentional cyber events from outside threat actors or internal resources that may, among other things, cause the Fund to lose proprietary information, suffer data corruption and/or destruction, lose operational capacity, result in the unauthorized release or other misuse of confidential information, or otherwise disrupt normal business operations. Cyber security breaches may involve unauthorized access to the Fund’s digital information systems (e.g., through “hacking” or malicious software coding), and may come from multiple sources, including outside attacks such as denial-of-service attacks (i.e., efforts to make network services unavailable to intended users) or cyber extortion, including exfiltration of data held for ransom and/or “ransomware” attacks that renders systems inoperable until ransom is paid, or insider actions. In addition, cyber security breaches involving the Fund’s third party service providers (including but not limited to advisers, sub-advisers, administrators, transfer agents, custodians, vendors, suppliers, distributors and other third parties), trading counterparties or issuers in which the Fund invests can also subject the Fund to many of the same risks associated with direct cyber security breaches or extortion of company data. Moreover, cyber security breaches involving trading counterparties or issuers in which the Fund invests could adversely impact such counterparties or issuers and cause the Fund’s investment to lose value.

shareholder transactions or otherwise transact business with shareholders; impediments to trading; violations of applicable privacy and other laws; regulatory fines; penalties; third party claims in litigation; reputational damage; reimbursement or other compensation costs; additional compliance and cyber security risk management costs and other adverse consequences. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future.

Like with operational risk in general, the Fund has established business continuity plans and risk management systems designed to reduce the risks associated with cyber security. However, there are inherent limitations in these plans and systems, including that certain risks may not have been identified, in large part because different or unknown threats may emerge in the future. As such, there is no guarantee that such efforts will succeed, especially because the Fund does not directly control the cyber security systems of issuers in which the Fund may invest, trading counterparties or third party service providers to the Fund. Such entities have experienced cyber attacks and other attempts to gain unauthorized access to systems from time to time, and there is no guarantee that efforts to prevent or mitigate the effects of such attacks or other attempts to gain unauthorized access will be successful. There is also a risk that cyber security breaches may not be detected. The Fund and its shareholders may suffer losses as a result of a cyber security breach related to the Fund, its service providers, trading counterparties or the issuers in which the Fund invests.

Potential Conflicts of Interest Risk—Allocation of Investment Opportunities.

The Investment Manager and its affiliates are involved worldwide with a broad spectrum of financial services and asset management activities and may engage in the ordinary course of business in activities in which their interests or the interests of their clients may conflict with those of the Fund. The Investment Manager may provide investment management services to other funds and discretionary managed accounts that follow an investment program similar to that of the Fund. Subject to the requirements of the 1940 Act, the Investment Manager intends to engage in such activities and may receive compensation from third parties for its services. The results of the Fund’s investment activities may differ from those of other accounts managed by the Investment Manager or its affiliates, and it is possible that the Fund could sustain losses during periods in which one or more other accounts managed by the Investment Manager or its affiliates, including proprietary accounts, achieve profits on their trading.

Repurchase Agreements Risk

The Fund may enter into repurchase agreements, in which the Fund purchases a security from a bank or broker-dealer, which agrees to repurchase the security at the Fund’s cost plus interest within a specified time. If the party agreeing to repurchase should default, the Fund will seek to sell the securities which it holds. This could involve procedural costs or delays in addition to a loss on the securities if their value should fall below their repurchase price. Repurchase agreements may be or become illiquid. These events could also trigger adverse tax consequences for the Fund.

15 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

Structured Investments Risk

Holders of structured products, including structured notes, credit-linked notes and other types of structured products, bear the risks of the underlying investments, index or reference obligation and are subject to counterparty risk. The Fund may have the right to receive payments only from the structured product, and generally does not have direct rights against the issuer or the entity that sold the assets to be securitized. Although it is difficult to predict whether the prices of indices and securities underlying structured products will rise or fall, these prices (and, therefore, the prices of structured products) are generally influenced by the same types of political and economic events that affect issuers of securities and capital markets generally. Structured products generally entail risks associated with derivative instruments.

Market Disruptions Risk

The Fund is subject to investment and operational risks associated with financial, economic and other global market developments and disruptions, including those arising from war, terrorism, market manipulation, government interventions, defaults and shutdowns, political changes or diplomatic developments, public health emergencies (such as the spread of infectious diseases, pandemics and epidemics) and natural/environmental disasters, which can all negatively impact the securities markets, interest rates, secondary trading, ratings, credit risk, inflation, deflation, other factors relating to the Fund’s investments or the Investment Manager’s operations and the value of an investment in the Fund, its distributions and its returns. These events can also impair the technology and other operational systems upon which the Fund’s service providers, including PIMCO as the Fund’s investment adviser, rely, and could otherwise disrupt the Fund’s service providers’ ability to fulfill their obligations to the Fund.

For example, the recent spread of an infectious respiratory illness caused by a novel strain of coronavirus (known as COVID-19) has caused volatility, severe market dislocations and liquidity constraints in many markets, including markets for the securities the Fund holds, and may adversely affect the Fund’s investments and operations.

The U.S. Federal Reserve made emergency interest-rate cuts, moving short-term rates to near zero, issued forward guidance that rates would remain low until the economy weathers the COVID-19 crisis, and resumed quantitative easing. Additionally, Congress approved stimulus to offset the severity and duration of the adverse economic effects of COVID-19 and related disruptions in economic and business activity. Dozens of central banks across Europe, Asia, and elsewhere have announced and/or adopted similar economic relief packages. The end of any such programs could cause market downturns, disruptions and volatility, particularly if markets view the ending as premature.

Certain Affiliations

affiliated brokers, and its ability to purchase securities being underwritten by an affiliated broker or a syndicate including an affiliated broker, or to utilize affiliated brokers for agency transactions, is subject to restrictions. This could limit the Fund’s ability to engage in securities transactions and take advantage of market opportunities.

Anti-Takeover Provisions

The Fund’s Amended and Restated Declaration of Trust (the “Declaration”) includes provisions that could limit the ability of other entities or persons to acquire control of the Fund or to convert the Fund to open-end status. See “Anti-Takeover and Other Provisions in the Declaration of Trust and Bylaws.” These provisions in the Declaration could have the effect of depriving the Common Shareholders of opportunities to sell their Common Shares at a premium over the then-current market price of the Common Shares or at NAV.

Distribution Rate Risk

Although the Fund may seek to maintain level distributions, the Fund’s distribution rates may be affected by numerous factors, including but not limited to changes in realized and projected market returns, fluctuations in market interest rates, Fund performance, and other factors. There can be no assurance that a change in market conditions or other factors will not result in a change in the Fund’s distribution rate or that the rate will be sustainable in the future.

For instance, during periods of low or declining interest rates, the Fund’s distributable income and dividend levels may decline for many reasons. For example, the Fund may have to deploy uninvested assets (whether from purchases of Fund shares, proceeds from matured, traded or called debt obligations or other sources) in new, lower yielding instruments. Additionally, payments from certain instruments that may be held by the Fund (such as variable and floating rate securities) may be negatively impacted by declining interest rates, which may also lead to a decline in the Fund’s distributable income and dividend levels.

AMT Bonds Risk

Investments by the Fund in AMT Bonds may expose the Fund to certain risks in addition to those typically associated with municipal bonds. Interest or principal on AMT Bonds paid out of current or anticipated revenues from a specific project or specific asset may be adversely impacted by declines in revenue from the project or asset. Declines in general business activity could also affect the economic viability of facilities that are the sole source of revenue to support AMT Bonds. In this regard, AMT Bonds may entail greater risks than general obligation municipal bonds. For shareholders subject to the federal alternative minimum tax, a portion of the Fund’s distributions may not be exempt from gross federal income, which may give rise to alternative minimum tax liability.

Focused Investment Risk

[ ] | Base Prospectus 16

PIMCO Municipal Income Fund

their ability to meet their obligations and the economic condition of the facility or specific revenue source from whose revenues payments of obligations may be made. The ability of state, county, or local governments or other issuers to meet their obligations will depend primarily on the availability of tax and other revenues to those entities. The amounts of tax and other revenues available to issuers may be affected from time to time by economic, political and demographic conditions that specifically impact such issuers. In addition, there are constitutional and statutory restrictions that limit the power of certain issuers to raise revenues or increase taxes. The availability of federal, state and local aid to issuers may also affect their ability to meet their obligations. The creditworthiness of obligations issued by local issuers within a given state may be unrelated to the creditworthiness of obligations issued by the state and there is no obligation on the part of the state to make payment on such local obligations in the event of default. Any reduction in the actual or perceived ability of an issuer to meet its obligations (including a reduction in the rating of its outstanding securities) would likely affect adversely the market value and marketability of its obligations and could adversely affect the values of other bonds as well. Moreover, in such circumstances, the value of the Fund’s shares may fluctuate more widely than the value of shares of a more diversified fund.

Many factors, including national economic, social and environmental policies and conditions, which are not within the control of issuers, could affect or could have an adverse impact on the financial condition of the issuers. The Fund is unable to predict whether or to what extent such factors or other factors may affect issuers, the market value or marketability of such bonds or the ability of the respective issuers of the bonds acquired by the Fund to pay interest on or principal of such bonds.

CSDR Related Risk

The European Union has adopted a settlement discipline regime under Regulation (EU) No 909/2014 and the Settlement Discipline RTS as they may be modified from time to time (“CSDR”), which will have phased compliance dates. It aims to reduce the number of settlement fails that occur in EEA central securities depositories (“CSDs”) and address settlement fails where they occur. The key elements of the regime are: (i) mandatory buy-ins—if a settlement fail continues for a specified period of time after the intended settlement date, a buy-in process must be initiated to effect the settlement; (ii) cash penalties—EEA CSDs are required to impose cash penalties on participants that cause settlement fails and distribute these to receiving participants; and (iii) allocations and confirmations—EEA investment firms are required to take measures to prevent settlement fails, including putting in place arrangements with their professional clients to communicate securities allocations and transaction confirmations. These requirements apply to transactions in transferable securities (e.g., shares and bonds), money market instruments, units in funds and emission allowances that are to be settled via an EEA CSD and, in the case of cash penalties and buy-in requirements only, are admitted to trading or traded on an EEA trading venue or cleared by an EEA central counterparty.

The implementation of the CSDR settlement discipline regime for funds that enter into in-scope transactions may result in increased operational and compliance costs being borne directly or indirectly by the Fund. CSDR may also affect liquidity and increase trading costs associated with relevant securities. If in-scope transactions are subject to additional expenses and penalties as a consequence of the CSDR settlement discipline regime, such expenses and penalties may be charged to the relevant Fund depending upon their characterization under the Fund’s Investment Management Agreement.

Insurance Risk

The Fund may purchase municipal securities that are secured by insurance, bank credit agreements or escrow accounts. The credit quality of the companies that provide such credit enhancements will affect the value of those securities. Certain significant providers of insurance for municipal securities have incurred significant losses as a result of exposure to sub-prime mortgages and other lower credit quality investments that have experienced recent defaults or otherwise suffered extreme credit deterioration. As a result, such losses reduced the insurers’ capital and called into question their continued ability to perform their obligations under such insurance if they are called upon to do so in the future. If the insurer of a municipal security suffers a downgrade in its credit rating or the market discounts the value of the insurance provided by the insurer, the rating of the underlying municipal security will be more relevant and the value of the municipal security would more closely, if not entirely, reflect such rating. In such a case, the value of insurance associated with a municipal security would decline and may not add any value. The insurance feature of a municipal security does not guarantee the full payment of principal and interest through the life of an insured obligation, the market value of the insured obligation or the net asset value of the common shares represented by such insured obligation.

Investing in the municipal bond market involves the risks of investing in debt securities generally and certain other risks. The amount of public information available about the municipal bonds in which the Fund may invest is generally less than that for corporate equities or bonds, and the investment performance of the Fund’s investment in municipal bonds may therefore be more dependent on the analytical abilities of PIMCO than its investments in taxable bonds. The secondary market for municipal bonds also tends to be less well developed or liquid than many other securities markets, which may adversely affect the Fund’s ability to sell municipal bonds at attractive prices.

17 Base Prospectus | PIMCO Municipal Income Fund

PIMCO Municipal Income Fund

Summary of Fund Expenses

The following table is intended to assist investors in understanding the fees and expenses (annualized) that an investor in Common Shares of the Fund would bear, directly or indirectly, as a result of an offering. The table reflects the use of leverage attributable to the Fund’s outstanding Preferred Shares and TOBs in an amount equal to [ ]% of the Fund’s total managed assets (including assets attributable to such leverage), which reflects approximately the percentage of the Fund’s total average managed assets attributable to such leverage averaged over the year ended June 30, 2022, and shows Fund expenses as a percentage of net assets attributable to Common Shares. The percentage above and information below do not reflect the Fund’s use of other forms of economic leverage, such as credit default swaps or other derivative instruments. The table and example below are based on the Fund’s capital structure as of June 30, 2022. The extent of the Fund’s assets attributable to leverage following an offering, and the Fund’s associated expenses, are likely to vary (perhaps significantly) from these assumptions.

Shareholder Transaction Expenses:

	Percentage of Offering Price
Sales Load (as a percentage of offering price)(1)	[-]%
Offering Expenses Borne by Common Shareholders (as a percentage of offering price)(2)	[-]%
Dividend Reinvestment Plan Fees(3)	None

(1)

In the event that the Common Shares to which this prospectus relates are sold to or through underwriters or dealer managers, a corresponding prospectus supplement will disclose the applicable sales load and/or commission.

(2)

The related prospectus supplement will disclose the estimated amount of offering expenses, the offering price and the offering expenses borne by the Fund and indirectly by all of its Common Shareholders as a percentage of the offering price.

(3)

You will pay brokerage charges if you direct your broker or the plan agent to sell your Common Shares that you acquired pursuant to a dividend reinvestment plan. You may also pay a pro rata share of brokerage commissions incurred in connection with open-market purchases pursuant to the Fund’s Dividend Reinvestment Plan. See “Dividend Reinvestment Plan.”

Annual Expenses

Annual Expenses	Percentage of Net Assets Attributable to Common Shares (reflecting leverage attributable to Preferred Shares and TOBs)
Management Fees(1)	[ ]%
Dividend Cost on Preferred Shares(2)	[ ]%
Interest Payments on Borrowed Funds(3)	[ ]%
Other Expenses(4)	[ ]%
Total Annual Expenses(5)	[ ]%

(1)

Management Fees include fees payable to the Investment Manager for advisory services and for supervisory, administrative and other services. The Fund pays for the advisory, supervisory and administrative services it requires under what is essentially an all-in fee structure (the “unified management fee”). Pursuant to an investment management agreement, PIMCO is paid a Management Fee of 0.705% of the Fund’s average daily net assets (including daily net assets attributable to any Preferred Shares). The Fund (and not PIMCO) will be responsible for certain fees and expenses, which are reflected in the table above, that are not covered by the unified management fee under the investment management agreement. Please see

“Management of the Fund–Investment Management Agreement” for an explanation of the unified management fee.

(2)

Restated to reflect the Fund’s outstanding ARPS and RVMTP averaged over the six-months ended June 30, 2022, which represented [ ]% and [ ]%, respectively, of the Fund’s total average managed assets (including the liquidation preference of outstanding Preferred Shares and assets attributable to TOBs), at an annual estimated dividend cost to the Fund of [ ]% for ARPS and [ ]% for RVMTP as of [ ], and assumes the Fund will continue to pay dividends on the ARPS at the “maximum applicable rate” called for under the Fund’s Bylaws due to the ongoing failure of auctions for the ARPS. The actual dividend rate paid on the Preferred Shares will vary over time in accordance with variations in market interest rates. See “Use of Leverage” and “Description of Capital Structure.”

(3)

Restated to reflect the Fund’s use of leverage in the form of TOBs averaged over the six-months ended June 30, 2022, which represented [ ]% of the Fund’s total average managed assets (including assets attributable to Preferred Shares and TOBs), at an estimated annual interest rate cost to the Fund of [ ]% as of June 30, 2022. See “Use of Leverage—Effects of Leverage.” The actual amount of interest expense borne by the Fund will vary over time in accordance with the level of the Fund’s use of Preferred Shares, TOBs and/or other forms of borrowing and variations in market interest rates. Borrowing expense is required to be treated as an expense of the Fund for accounting purposes. Any associated income or gains (or losses) realized from leverage obtained through such instruments is not reflected in the Annual Expenses table above, but would be reflected in the Fund’s performance results.

(4)

“Other Expenses” are estimated for the Fund’s current fiscal year ending December 31, 2022.

(5)

“Dividend Cost on Preferred Shares”, including distributions on Preferred Shares, and “Interest Payments on Borrowed Funds” are borne by the Fund separately from the management fees paid to PIMCO. Excluding such expenses, Total Annual Expenses are [ ]%.

Example

The following example illustrates the expenses that you would pay on a $1,000 investment in Common Shares of the Fund, assuming (1) that the Fund’s net assets do not increase or decrease, (2) that the Fund incurs total annual expenses of [ ]% of net assets attributable to Common Shares in years 1 through 10 (assuming outstanding Preferred Shares and TOBs representing [ ]% of Fund total managed assets) and (3) a 5% annual return(1):

	1 Year	3 Years	5 Years	10 Years
Total Expenses Incurred	[ ]	[ ]	[ ]	[ ]

(1)

The example above should not be considered a representation of future expenses. Actual expenses may be higher or lower than those shown. The example assumes that the estimated Interest Payments on Borrowed Funds, Dividend Cost on Preferred Shares and Other Expenses set forth in the Annual Expenses table are accurate, that the rate listed under Total Annual Expenses remains the same each year and that all dividends and distributions are reinvested at NAV. Actual expenses may be greater or less than those assumed. Moreover, the Fund’s actual rate of return may be greater or less than the hypothetical 5% annual return shown in the example. The example does not include commissions or estimated offering expenses, which would cause the expenses shown in the example to increase. In connection with an offering of Common Shares, the prospectus supplement will set forth an example including sales load and estimated offering costs.

PIMCO Municipal Income Fund | Base Prospectus 18

Base Prospectus

Use of Proceeds

The net proceeds of an offering will be invested in accordance with the Fund’s investment objective and policies as set forth below. It is currently anticipated that the Fund will be able to invest substantially all of the net proceeds of an offering in accordance with its investment objective and policies within approximately 30 days of receipt by the Fund, depending on the amount and timing of proceeds available to the Fund as well as the availability of investments consistent with the Fund’s investment objective and policies, and except to the extent proceeds are held in cash to pay dividends or expenses, or for temporary defensive purposes. Pending such investment, it is anticipated that the proceeds of an offering will be invested in high grade, short-term securities, credit-linked trust certificates, and/or high yield securities index futures contracts or similar derivative instruments designed to give the Fund exposure to the securities and markets in which it intends to invest while the Investment Manager selects specific investments.

The Fund

The Fund is a diversified, closed-end management investment company. The Fund was organized as a Massachusetts business trust on May 9, 2001, pursuant to an Agreement and Declaration of Trust governed by the laws of the Commonwealth of Massachusetts. The Fund commenced operations on June 29, 2001, following the initial public offering of its Common Shares.

Investment Objective and Policies

Portfolio Investment Strategies

Under normal circumstances, the Fund expects to invest at least 90% of its net assets in municipal bonds which pay interest that, in the opinion of bond counsel to the issuer (or on the basis of other authority believed by PIMCO to be reliable), is exempt from regular federal income taxes (i.e., excluded from gross income for federal income tax purposes but not necessarily exempt from the federal alternative minimum tax). Subject to its other investment policies, the Fund may invest up to 20% of its total assets in investments the interest from which is subject to the federal alternative minimum tax.

invest up to 20% of its net assets in municipal bonds that are, at the time of investment, rated Ba/BB or B or lower by Moody’s, S&P or Fitch or that are unrated but judged to be of comparable quality by PIMCO. Bonds of below investment grade quality are regarded as having predominantly speculative characteristics with respect to capacity to pay interest and repay principal, and are commonly referred to as “junk bonds.” Bonds in the lowest investment grade category may also be considered to possess some speculative characteristics.

Portfolio Contents

Also included within the general category of municipal bonds in which the Fund may invest are participations in lease obligations.

[ ] | Base Prospectus 20

PIMCO Municipal Income Fund

The Fund may invest in trust certificates issued in TOB programs. In these programs, a trust typically issues two classes of certificates, floating rate certificates (“TOB Floaters”) and residual interest certificates (“TOB Residuals”), and seeks to use the proceeds to purchase municipal securities having longer maturities and bearing interest at a higher fixed interest rate than prevailing short-term tax-exempt rates. Service providers of such trusts may have recourse against the Fund in certain cases, such as if the Fund holds recourse TOB Residuals. The Fund may invest in both non-recourse and recourse TOB Residuals to leverage its portfolio.

described above. In addition, failure to comply with these limitations and restrictions could, among other things, preclude the Fund from declaring or paying dividend or distributions.

The following provides additional information regarding the types of securities and other instruments in which the Fund will ordinarily invest. A more detailed discussion of these and other instruments and investment techniques that may be used by the Fund is provided under “Investment Objective and Policies” in the Statement of Additional Information.

Municipal Bonds

Municipal bonds share the attributes of debt/fixed income securities in general, but are generally issued by states, municipalities and other political subdivisions, agencies, authorities and instrumentalities of states and multi-state agencies or authorities, and may be either taxable or tax-exempt instruments. The municipal bonds that the Fund may purchase include, without limitation, general obligation bonds and limited obligation bonds (or revenue bonds), including industrial development bonds issued pursuant to former federal tax law. General obligation bonds are obligations involving the credit of an issuer possessing taxing power and are payable from such issuer’s general revenues and not from any particular source. Limited obligation bonds are payable only from the revenues derived from a particular facility or class of facilities or, in some cases, from the proceeds of a special excise or other specific revenue source or annual revenues. Private activity bonds and industrial development bonds generally are also limited obligation bonds and thus are not payable from the issuer’s general revenues. The credit and quality of private activity bonds and industrial development bonds are usually related to the credit of the corporate user of the facilities. Payment of interest on and repayment of principal of such bonds is the responsibility of the corporate user (and/or any guarantor).

The Fund may invest in Build America Bonds, which are tax credit bonds created by the American Recovery and Reinvestment Act of 2009, which authorizes state and local governments to issue Build America Bonds as taxable bonds in 2009 and 2010, without volume limitations, to finance any capital expenditures for which such issuers could otherwise issue traditional tax-exempt bonds. State and local governments may receive a direct federal subsidy payment for a portion of their borrowing costs on Build America Bonds equal to 35% of the total coupon interest paid to investors (or 45% in the case of Recovery Zone Economic Development Bonds). The state or local government issuer can elect to either take the federal subsidy or pass the 35% tax credit along to bondholders. The Fund’s investments in Build America Bonds will result

21 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

in taxable income and the Fund may elect to pass through to shareholders the corresponding tax credits. The tax credits can generally be used to offset federal income taxes and the alternative minimum tax, but such credits are generally not refundable. Build America Bonds involve similar risks as municipal bonds, including credit and market risk. They are intended to assist state and local governments in financing capital projects at lower borrowing costs and are likely to attract a broader group of investors than tax-exempt municipal bonds. For example, taxable funds, such as the Fund, may choose to invest in Build America Bonds. Although Build America Bonds were only authorized for issuance during 2009 and 2010, the program may have resulted in reduced issuance of tax-exempt municipal bonds during the same period. The Build America Bond program expired on December 31, 2010, at which point no further issuance of new Build America Bonds was permitted. As of the date of this prospectus, there is no indication that Congress will renew the program to permit issuance of new Build America Bonds.

The Fund may invest in pre-refunded municipal bonds. Pre-refunded municipal bonds are bonds that have been refunded to a call date prior to the final maturity of principal, or, in the case of pre-refunded municipal bonds commonly referred to as “escrowed-to-maturity bonds,” to the final maturity of principal, and remain outstanding in the municipal market. The payment of principal and interest of the pre-refunded municipal bonds held by the Fund is funded from securities in a designated escrow account that holds U.S. Treasury securities or other obligations of the U.S. government (including its agencies and instrumentalities (“Agency Securities”)). Interest payments on pre-funded municipal bonds issued on or prior to December 31, 2017 are exempt from federal income tax; pre-funded municipal bonds issued after December 31, 2017 will not qualify for such tax-advantaged treatment. Pre-refunded municipal bonds usually will bear an AAA/Aaa rating (if rerated by Fitch, Moody’s or S&P or if determined by PIMCO to be of comparable quality) because they are backed by U.S. Treasury securities or Agency Securities. Because the payment of principal and interest is generated from securities held in an escrow account established by the municipality and an independent escrow agent, the pledge of the municipality has been fulfilled and the original pledge of revenue by the municipality is no longer in place. The escrow account securities pledged to pay the principal and interest of the pre-refunded municipal bond do not guarantee the price movement of the bond before maturity. Issuers of municipal bonds refund in advance of maturity the outstanding higher cost debt and issue new, lower cost debt, placing the proceeds of the lower cost issuance into an escrow account to pre-refund the older, higher cost debt. Investment in pre-refunded municipal bonds held by the Fund may subject the Fund to interest rate risk and market risk. In addition, while a secondary market exists for pre-refunded municipal bonds, if the Fund sells pre-refunded municipal bonds prior to maturity, the price received may be more or less than the original cost, depending on market conditions at the time of sale.

The Fund may invest in municipal lease obligations. A lease is not a full faith and credit obligation of the issuer and is usually backed only by the borrowing government’s unsecured pledge to make annual

appropriations for lease payments. There have been challenges to the legality of lease financing in numerous states, and, from time to time, certain municipalities have considered not appropriating money for lease payments. In deciding whether to purchase a lease obligation for the Fund, PIMCO will assess the financial condition of the borrower or obligor, the merits of the project, other credit characteristics of the obligor, the level of public support for the project and the legislative history of lease financing in the state. These securities may be less readily marketable than other municipal securities.

Some longer-term municipal bonds give the investor the right to “put” or sell the security at par (face value) within a specified number of days following the investor’s request-usually one to seven days. This demand feature enhances a security’s liquidity by shortening its effective maturity and enables it to trade at a price equal to or very close to par. If a demand feature terminates prior to being exercised, the Fund would hold the longer-term security, which could experience substantially more volatility.

The Fund may invest in municipal warrants, which are essentially call options on municipal bonds. In exchange for a premium, municipal warrants give the purchaser the right, but not the obligation, to purchase a municipal bond in the future. The Fund may purchase a warrant to lock in forward supply in an environment in which the current issuance of bonds is sharply reduced. Like options, warrants may expire worthless and may have reduced liquidity.

The Fund may invest in municipal bonds with credit enhancements such as letters of credit, municipal bond insurance and standby bond purchase agreements (“SBPAs”). Letters of credit are issued by a third party, usually a bank, to enhance liquidity and to ensure repayment of principal and any accrued interest if the underlying municipal bond should default. Municipal bond insurance, which is usually purchased by the bond issuer from a private, nongovernmental insurance company, provides an unconditional and irrevocable guarantee that the insured bond’s principal and interest will be paid when due. Insurance does not guarantee the price of the bond. The credit rating of an insured bond reflects the credit rating of the insurer, based on its claims-paying ability. The obligation of a municipal bond insurance company to pay a claim extends over the life of each insured bond. Although defaults on insured municipal bonds have been low to date and municipal bond insurers have met their claims, there is no assurance that this will continue. A higher-than expected default rate could strain the insurer’s loss reserves and adversely affect its ability to pay claims to bondholders. Because a significant portion of insured municipal bonds that have been issued and are outstanding is insured by a small number of insurance companies, not all of which have the highest credit rating, an event involving one or more of these insurance companies, such as a credit rating downgrade, could have a significant adverse effect on the value of the municipal bonds insured by such insurance company or companies and on the municipal bond markets as a whole. An SBPA is a liquidity facility provided to pay the purchase price of bonds that cannot be re-marketed. The obligation of the liquidity provider (usually a bank) is only to advance funds to purchase tendered bonds that cannot be re-marketed and does not cover principal or interest under any other

[ ] | Base Prospectus 22

PIMCO Municipal Income Fund

circumstances. The liquidity provider’s obligations under the SBPA are usually subject to numerous conditions, including the continued creditworthiness of the underlying borrower.

Tender Option Bonds

The Fund may invest in trust certificates issued in TOB programs. In a TOB transaction, a TOB Trust issues a TOB Floater and a TOB Residual and utilizes the proceeds of such issuance to purchase a Fixed Rate Bond that either is owned or identified by the Fund. The TOB Floater is generally issued to third party investors (typically a money market fund) and the TOB Residual is generally issued to the Fund, which sold or identified the Fixed Rate Bond. The TOB Trust divides the income stream provided by the Fixed Rate Bond to create two securities, the TOB Floater, which is a short-term security, and the TOB Residual, which is a longer-term security. The interest rates payable on the TOB Residual issued to the Fund bear an inverse relationship to the interest rate on the TOB Floater. The interest rate on the TOB Floater is reset by a remarketing process typically every 7 to 35 days. After income is paid on the TOB Floater at current rates, the residual income from the Fixed Rate Bond goes to the TOB Residual. Therefore, rising short-term rates result in lower income for the TOB Residual, and vice versa. In the case of a TOB Trust that utilizes the cash received (less transaction expenses) from the issuance of the TOB Floater and TOB Residual to purchase the Fixed Rate Bond from the Fund, the Fund may then invest the cash received in additional securities, generating leverage for the Fund. Other PIMCO-managed accounts may also contribute municipal bonds to a TOB Trust into which the Fund has contributed Fixed Rate Bonds. If multiple PIMCO-managed accounts participate in the same TOB Trust, the economic rights and obligations under the TOB Residual will be shared among the funds ratably in proportion to their participation in the TOB Trust.

The TOB Residual may be more volatile and less liquid than other municipal bonds of comparable maturity. In most circumstances the TOB Residual holder bears substantially all of the underlying Fixed Rate Bond’s downside investment risk and also benefits from any appreciation in the value of the underlying Fixed Rate Bond. Investments in a TOB Residual typically will involve greater risk than investments in Fixed Rate Bonds.

A TOB Residual held by the Fund provides the Fund with the right to: (1) cause the holders of the TOB Floater to tender their notes at par, and (2) cause the sale of the Fixed Rate Bond held by the TOB Trust, thereby collapsing the TOB Trust. TOB Trusts are generally supported by a liquidity facility provided by a third party bank or other financial institution (the “Liquidity Provider”) that provides for the purchase of TOB Floaters that cannot be remarketed. The holders of the TOB Floaters have the right to tender their certificates in exchange for payment of par plus accrued interest on a periodic basis (typically weekly) or on the occurrence of certain mandatory tender events. The tendered TOB Floaters are remarketed by a remarketing agent, which is typically an affiliated entity of the Liquidity Provider. If the TOB Floaters cannot be remarketed, the TOB Floaters are purchased by the TOB Trust either from the proceeds of a loan from the Liquidity Provider or from a liquidation of the Fixed Rate Bond.

The TOB Trust may also be collapsed without the consent of the Fund, as the TOB Residual holder, upon the occurrence of certain “tender option termination events” (or “TOTEs”) as defined in the TOB Trust agreements. Such termination events typically include the bankruptcy or default of the municipal bond, a substantial downgrade in credit quality of the municipal bond, or a judgment or ruling that interest on the Fixed Rate Bond is subject to federal income taxation. Upon the occurrence of a termination event, the TOB Trust would generally be liquidated in full with the proceeds typically applied first to any accrued fees owed to the trustee, remarketing agent, and liquidity provider, and then to the holders of the TOB Floater up to par plus accrued interest owed on the TOB Floater and a portion of gain share, if any, with the balance paid out to the TOB Residual holder. In the case of a mandatory termination event, after the payment of fees, the TOB Floater holders would be paid before the TOB Residual holders (i.e., the Fund). In contrast, in the case of a TOTE, after payment of fees, the TOB Floater holders and the TOB Residual holders would be paid pro rata in proportion to the respective face values of their certificates.

If there are insufficient proceeds from the liquidation of the TOB Trust, the party that would bear the losses would depend upon whether the Fund holds a non-recourse TOBs Residual or a recourse TOBs Residual. If the Fund holds a non-recourse TOBs Residual, the Liquidity Provider or holders of the TOBs Floaters would bear the losses on those securities and there would be no recourse to the Fund’s assets. If the Fund holds a recourse TOBs Residual, the Fund (and, indirectly, holders of the Fund’s Common Shares) would typically bear the losses. In particular, if the Fund holds a recourse TOBs Residual, it will typically have entered into an agreement pursuant to which the Fund would be required to pay to the Liquidity Provider the difference between the purchase price of any TOBs Floaters put to the Liquidity Provider by holders of the TOBs Floaters and the proceeds realized from the remarketing of those TOBs Floaters or the sale of the assets in the TOBs Issuer. The Fund may invest in both non-recourse and recourse TOBs Residuals to leverage its portfolio.

In December 2013, regulators finalized rules implementing Section 619 (the “Volcker Rule”) and Section 941 (the “Risk Retention Rules”) of the Dodd-Frank Act. Both the Volcker Rule and the Risk Retention Rules apply to TOB programs. In particular, these rules preclude banking entities from (i) sponsoring or acquiring interests in the trusts used to hold a municipal bond in the creation of TOB Trusts; and (ii) continuing to service or maintain relationships with existing programs involving TOB Trusts to the same extent and in the same capacity as existing programs. The Risk Retention Rules require the sponsor to a TOB Trust to retain at least five percent of the credit risk of the underlying assets supporting to the TOB Trust’s municipal bonds. The Risk Retention Rules may increase the costs of such transactions in certain circumstances.

In response to these rules, industry participants explored various structuring alternatives for TOB Trusts established after December 31, 2013 and TOB Trusts established prior to December 31, 2013 (“Legacy TOB Trusts”) and agreed on a new TOB structure in which the Fund hires service providers to assist with establishing, structuring, and sponsoring

23 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

a TOB Trust. Service providers to a TOB Trust, such as administrators, liquidity providers, trustees, and remarketing agents act at the direction of, and as agent of, the Fund as the TOB Residual holder.

Under the new TOB Trust structure, the Liquidity Provider or remarketing agent will no longer purchase the tendered TOB Floaters, even in the event of failed remarketing. This may increase the likelihood that a TOB Trust will need to be collapsed and liquidated in order to purchase the tendered TOB Floaters. The TOB Trust may draw upon a loan from the Liquidity Provider to purchase the tendered TOB Floaters. Any loans made by the Liquidity Provider will be secured by the purchased TOB Floaters held by the TOB Trust and will be subject to an interest rate agreed with the Liquidity Provider.

Bonds

The Fund may invest in bonds of varying maturities issued by non-U.S. (foreign) and U.S. corporations and other business entities, governments and quasi-governmental entities and municipalities and other issuers. Bonds may include, among other things, fixed or variable/floating-rate debt obligations, including bills, notes, debentures, money market instruments and similar instruments and securities. Bonds generally are used by corporations as well as governments and other issuers to borrow money from investors. The issuer pays the investor a fixed or variable rate of interest and normally must repay the amount borrowed on or before maturity. Certain bonds are “perpetual” in that they have no maturity date.

Commercial Paper

Commercial paper represents short-term unsecured promissory notes issued in bearer form by corporations such as banks or bank holding companies and finance companies. The rate of return on commercial paper may be linked or indexed to the level of exchange rates between the U.S. dollar and a foreign currency or currencies.

U.S. Government Securities

U.S. government securities are obligations of and, in certain cases, guaranteed by, the U.S. government, its agencies or instrumentalities. The U.S. government does not guarantee the NAV of the Fund’s common shares. Some U.S. government securities, such as Treasury bills, notes and bonds, and securities guaranteed by the Government National Mortgage Association, are supported by the full faith and credit of the United States; others, such as those of the Federal Home Loan Banks, are supported by the right of the issuer to borrow from the U.S. Department of the Treasury (the “U.S. Treasury”); others, such as those of the Federal National Mortgage Association, are supported by the discretionary authority of the U.S. government to purchase the agency’s obligations; and still others are supported only by the credit of the instrumentality. U.S. government securities may include zero coupon securities, which do not distribute interest on a current basis and tend to be subject to greater risk than interest-paying securities of similar maturities.

High Yield Securities

The Fund may invest up to 20% of its net assets in municipal bonds that are, at the time of purchase, rated below “investment grade” by at least one of Moody’s, S&P Global Ratings or Fitch, or unrated but determined by PIMCO to be of comparable quality. “Investment grade” means a rating, in the case of Moody’s, of Baa3 or higher, in the case of S&P and Fitch, of BBB-or higher. The Fund may invest in securities of stressed or distressed issuers, which include securities at risk of being in default as to the repayment of principal and/or interest at the time of acquisition by the Fund or that are rated in the lower rating categories by one or more nationally recognized statistical rating organizations (for example, Ca or lower by Moody’s or CC or lower by S&P or Fitch) or, if unrated, are determined by PIMCO to be of comparable quality. The Fund may invest in defaulted securities and debtor-in-possession financings. Below investment grade securities are commonly referred to as “high yield” securities or “junk bonds.” High yield securities involve a greater degree of risk (in particular, a greater risk of default) than, and special risks in addition to, the risks associated with investment grade debt obligations. While offering a greater potential opportunity for capital appreciation and higher yields, high yield securities typically entail greater potential price volatility and may be less liquid than higher-rated securities. High yield securities may be regarded as predominantly speculative with respect to the issuer’s continuing ability to make timely principal and interest payments. They also may be more susceptible to real or perceived adverse economic and competitive industry conditions than higher-rated securities. Debt securities in the lowest investment grade category also may be considered to possess some speculative characteristics by certain ratings agencies.

The market values of high yield securities tend to reflect individual developments of the issuer to a greater extent than do higher-quality securities, which tend to react mainly to fluctuations in the general level of interest rates. In addition, lower-quality debt securities tend to be more sensitive to general economic conditions. Certain emerging market governments that issue high yield securities in which the Fund may invest are among the largest debtors to commercial banks, foreign governments and supranational organizations, such as the World Bank, and may not be able or willing to make principal and/or interest payments as they come due.

Credit ratings and unrated securities. Rating agencies are private services that provide ratings of the credit quality of debt obligations. Appendix A to this prospectus describes the various ratings assigned to debt obligations by Moody’s, S&P and Fitch. As noted in Appendix A, Moody’s, S&P and Fitch may modify their ratings of securities to show relative standing within a rating category, with the addition of numerical modifiers (1, 2 or 3) in the case of Moody’s, and with the addition of a plus (+) or minus (-) sign in the case of S&P and Fitch. Ratings assigned by a rating agency are not absolute standards of credit quality and do not evaluate market risks. Rating agencies may fail to make timely changes in credit ratings and an issuer’s current financial condition may be better or worse than a rating indicates. The Fund will not necessarily sell a security when its rating is reduced below its rating

[ ] | Base Prospectus 24

PIMCO Municipal Income Fund

at the time of purchase. PIMCO does not rely solely on credit ratings, and develops its own analysis of issuer credit quality.

The ratings of a debt security may change over time. Moody’s, S&P and Fitch monitor and evaluate the ratings assigned to securities on an ongoing basis. As a result, debt instruments held by the Fund could receive a higher rating (which would tend to increase their value) or a lower rating (which would tend to decrease their value) during the period in which they are held by the Fund.

The Fund may purchase unrated securities (which are not rated by a rating agency) if PIMCO determines, in its sole discretion, that the security is of comparable quality to a rated security that the Fund may purchase. In making these determinations, PIMCO may take into account different factors than those taken into account by rating agencies, and PIMCO’s rating of a security may differ from the rating that a rating agency may have given the same security. Unrated securities may be less liquid than comparable rated securities and involve the risk that the portfolio manager may not accurately evaluate the security’s comparative credit rating. The Fund may invest a substantial portion of its assets in unrated securities and therefore may be particularly subject to the associated risks. Analysis of the creditworthiness of issuers of high yield securities may be more complex than for issuers of higher-quality fixed income securities. To the extent that the Fund invests in high yield and/or unrated securities, the Fund’s success in achieving its investment objective may depend more heavily on the portfolio manager’s credit analysis than if the Fund invested exclusively in higher-quality and higher-rated securities.

Mortgage-Related and Other Asset-Backed Instruments

The Fund may invest in a variety of mortgage-related and other asset-backed instruments issued by government agencies or other governmental entities or by private originators or issuers.

The mortgage-related assets in which the Fund may invest include, without limitation, mortgage pass-through securities, CMOs, CMBS, residential mortgage-backed securities (“RMBS”), mortgage dollar rolls/buy backs, CMO residuals, adjustable rate mortgage-backed securities (“ARMBS”), stripped mortgage-backed securities (“SMBS”) and other securities that directly or indirectly represent a participation in, or are secured by and payable from, mortgage loans on real property. The Fund may also invest in other types of ABS, including CDOs, which include CBOs, CLOs and other similarly structured securities. The mortgage-related securities in which the Fund may invest may pay variable or fixed rates of interest. When acquiring mortgage-related or other ABS, the Fund is not restricted by any particular borrower credit criteria. Accordingly, loans underlying mortgage-related securities acquired by the Fund may be subprime in quality, or may become subprime in quality. Mortgage-related securities are not traded on an exchange and there may be a limited market for the securities, especially when there is a perceived weakness in the mortgage and real estate market sectors. Without an active trading market, mortgage-related securities held in the Fund’s portfolio may be particularly difficult to value because of the complexities involved in assessing the value of the underlying mortgage loans.

Mortgage-Related Derivative Instruments

The Fund may engage in derivative transactions related to mortgage-backed securities, including purchasing and selling exchange-listed and OTC put and call options, futures and forwards on mortgages and mortgage-backed securities. The Fund may also invest in mortgage-backed securities credit default swaps, which include swaps the reference obligation for which is a mortgage-backed security or related index, such as the CMBX Index (a tradeable index referencing a basket of commercial mortgage-backed securities), the TRX Index (a tradeable index referencing total return swaps based on commercial mortgage-backed securities) or the ABX (a tradeable index referencing a basket of sub-prime mortgage-backed securities). The Fund may invest in newly developed mortgage related derivatives that may hereafter become available.

Please see “Investment Objective and Policies—Mortgage-Related and Other Asset-Backed Instruments” in the Statement of Additional Information and “Principal Risks of the Fund—Mortgage-Related and Asset-Backed Instruments Risk” in this prospectus for a more detailed description of the types of mortgage-related and other asset-backed securities in which the Fund may invest and their related risks.

Variable- and Floating-Rate Securities

Variable- and floating-rate instruments are instruments that pay interest at rates that adjust whenever a specified interest rate changes and/or that reset on predetermined dates (such as the last day of a month or calendar quarter). In addition to senior loans, variable- and floating-rate instruments may include, without limitation, instruments such as catastrophe and other event-linked bonds, instruments such as bank capital securities, unsecured bank loans, corporate bonds, money market instruments and certain types of mortgage-related and other asset-backed securities. Due to their variable- or floating-rate features, these instruments will generally pay higher levels of income in a rising interest rate environment and lower levels of income as interest rates decline. For the same reason, the market value of a variable- or floating-rate instrument is generally expected to have less sensitivity to fluctuations in market interest rates than a fixed-rate instrument, although the value of a variable- or floating-rate instrument may nonetheless decline as interest rates rise and due to other factors, such as changes in credit quality.

The Fund also may engage in credit spread trades. A credit spread trade is an investment position relating to a difference in the prices or interest rates of two bonds or other securities, in which the value of the investment position is determined by changes in the difference between the prices or interest rates, as the case may be, of the respective securities.

Inverse Floaters

An inverse floater is a type of debt instrument that bears a floating or variable interest rate that moves in the opposite direction to interest rates generally or the interest rate on another security or index. Changes in interest rates generally, or the interest rate of the other security or index, inversely affect the interest rate paid on the inverse floater, with

25 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

the result that the inverse floater’s price will be considerably more volatile than that of a fixed-rate bond. The Fund may invest without limitation in inverse floaters, which brokers typically create by depositing an income-producing instrument, which may be a mortgage-related security, in a trust. The trust in turn issues a variable rate security and inverse floaters. The interest rate for the variable rate security is typically determined by an index or an auction process, while the inverse floater holder receives the balance of the income from the underlying income-producing instrument less an auction fee. The market prices of inverse floaters may be highly sensitive to changes in interest rates and prepayment rates on the underlying securities, and may decrease significantly when interest rates increase or prepayment rates change. In a transaction in which the Fund purchases an inverse floater from a trust, and the underlying bond was held by the Fund prior to being deposited into the trust, the Fund will typically treat the transaction as a secured borrowing for financial reporting purposes. As a result, for financial reporting purposes, the Fund will generally incur a non-cash interest expense with respect to interest paid by the trust on the variable rate securities, and will recognize additional interest income in an amount directly corresponding to the non-cash interest expense. Therefore, the Fund’s NAV per Common Share and performance will not be affected by the non-cash interest expense. This accounting treatment does not apply to inverse floaters acquired by the Fund when the Fund did not previously own the underlying bond.

Derivatives

The Fund may, but is not required to, use various derivative instruments for risk management purposes or as part of its investment strategy. The Fund may use various derivatives transactions to add leverage to its portfolio. See “Use of Leverage.”

Generally, derivatives are financial contracts whose value depends upon, or is derived from, the value of an underlying asset, reference rate or index, and may relate to, among others, stocks, bonds, real estate investments, interest rates, spreads between different interest rates, currencies or currency exchange rates, commodities and related indexes. Examples of derivative instruments that the Fund may use include, without limitation, futures and forward contracts (including foreign currency exchange contracts), call and put options (including options on futures contracts), credit default swaps, total return swaps, basis swaps and other swap agreements. The Fund’s use of derivative instruments involves risks different from, or possibly greater than, the risks associated with investing directly in securities and other more traditional investments. Please see “Principal Risks of the Fund—Derivatives Risk” in this Prospectus and see “Investment Objective and Policies—Derivative Instruments” in the Statement of Additional Information for additional information about these and other derivative instruments that the Fund may use and the risks associated with such instruments. There is no assurance that these derivative strategies will be available at any time or that PIMCO will determine to use them for the Fund or, if used, that the strategies will be successful. In

addition, the Fund may be subject to certain restrictions on its use of derivative strategies imposed by guidelines of one or more rating agencies that may issue ratings for any preferred shares issued by the Fund.

Certain Interest Rate Transactions

In order to reduce the interest rate risk inherent in the Fund’s underlying investments and capital structure, the Fund may (but is not required to) enter into interest rate swap transactions. Interest rate swaps involve the exchange by the Fund with a counterparty of their respective commitments to pay or receive interest, such as an exchange of fixed rate payments for floating rate payments. These transactions generally involve an agreement with the swap counterparty to pay a fixed or variable rate payment in exchange for the counterparty paying the Fund the other type of payment stream (i.e., variable or fixed). The payment obligation would be based on the notional amount of the swap. Other forms of interest rate swap agreements in which the Fund may invest include without limitation interest rate caps, under which, in return for a premium, one party agrees to make payments to the other to the extent that interest rates exceed a specified rate, or “cap;” interest rate floors, under which, in return for a premium, one party agrees to make payments to the other to the extent that interest rates fall below a specified rate, or “floor;” and interest rate “collars,” under which a party sells a cap and purchases a floor or vice versa in an attempt to protect itself against interest rate movements exceeding given minimum or maximum levels. The Fund may (but is not required to) use interest rate swap transactions with the intent to reduce or eliminate the risk that an increase in short-term interest rates could pose for the performance of the Fund's Common Shares as a result of leverage, and also may use these instruments for other hedging or investment purposes. Any termination of an interest rate swap transaction could result in a termination payment by or to the Fund.

Credit Default Swaps

The Fund may enter into credit default swaps for both investment and risk management purposes, as well as to add leverage to the Fund’s portfolio. A credit default swap may have as reference obligations one or more securities that are not currently held by the Fund. The protection “buyer” in a credit default swap is generally obligated to pay the protection “seller” an upfront or a periodic stream of payments over the term of the contract provided that no credit event, such as a default, on a reference obligation has occurred. If a credit event occurs, the seller generally must pay the buyer the “par value” (full notional value) of the swap in exchange for an equal face amount of deliverable obligations of the reference entity described in the swap, or the seller may be required to deliver the related net cash amount, if the swap is cash settled. Rather than exchange the bonds for par value, a single cash payment may be due from the protection seller representing the difference between the par value of the bonds and the current market value of the bonds (which may be determined through an auction). The Fund may be either the buyer or seller in the transaction. If the Fund is a buyer and no credit event occurs, the Fund may recover nothing if the swap is held through its termination date. However, if a credit event occurs, the buyer

[ ] | Base Prospectus 26

PIMCO Municipal Income Fund

generally may elect to receive the full notional value of the swap from the seller, who, in turn, generally will recover an amount significantly lower than the equivalent face amount of the obligations of the reference entity, whose value may have significantly decreased, through (i) physical delivery of such obligations by the buyer, (ii) cash settlement or (iii) an auction process. As a seller, the Fund generally receives an upfront payment or a fixed rate of income throughout the term of the swap provided that there is no credit event. As the seller, the Fund would effectively add leverage to its portfolio because, in addition to its total net assets, the Fund would be subject to investment exposure on the notional amount of the swap.

The spread of a credit default swap is the annual amount the protection buyer must pay the protection seller over the length of the contract, expressed as a percentage of the notional amount. When spreads rise, market perceived credit risk rises and when spreads fall, market perceived credit risk falls. Wider credit spreads and decreasing market values, when compared to the notional amount of the swap, represent a deterioration of the referenced entity’s credit soundness and a greater likelihood or risk of default or other credit event occurring as defined under the terms of the agreement. For credit default swaps on ABS and credit indexes, the quoted market prices and resulting values, as well as the annual payment rate, serve as an indication of the current status of the payment/performance risk.

Credit default swaps involve greater risks than if the Fund had invested in the reference obligation directly since, in addition to general market risks, credit default swaps are subject to illiquidity risk, counterparty risk and credit risk, among other risks associated with derivative instruments. A buyer generally also will lose the upfront and/or periodic payments it made for the swap and recover nothing should no credit event occur and the swap is held to its termination date. If a credit event were to occur, the value of any deliverable obligation received by the seller, coupled with the upfront or periodic payments previously received, may be less than the full notional value it pays to the buyer, resulting in a loss of value to the seller. The Fund’s obligations under a credit default swap will be accrued daily (offset against any amounts owing to the Fund). In connection with credit default swaps in which the Fund is the buyer, the Fund may segregate or “earmark” cash or liquid assets, or enter into certain offsetting positions, with a value at least equal to the Fund’s exposure (any accrued but unpaid net amounts owed by the Fund to any counterparty), on a marked-to-market basis.

Structured Notes and Related Instruments

The Fund may invest in “structured” notes and other related instruments, which are privately negotiated debt obligations in which the principal and/or interest is determined by reference to the performance of a benchmark asset, market or interest rate (an “embedded index”), such as selected securities, an index of securities or specified interest rates, or the differential performance of two assets or markets, such as indexes reflecting bonds. Structured instruments may be issued by corporations, including banks, as well as by governmental agencies. Structured instruments frequently are assembled in the form of medium-term notes, but a variety of forms are available and may be used in particular circumstances. The terms of such structured

instruments normally provide that their principal and/or interest payments are to be adjusted upwards or downwards (but ordinarily not below zero) to reflect changes in the embedded index while the structured instruments are outstanding. As a result, the interest and/or principal payments that may be made on a structured product may vary widely, depending on a variety of factors, including the volatility of the embedded index and the effect of changes in the embedded index on principal and/or interest payments. The rate of return on structured notes may be determined by applying a multiplier to the performance or differential performance of the referenced index(es) or other asset(s). Application of a multiplier involves leverage that will serve to magnify the potential for gain and the risk of loss.

The Fund may use structured instruments for investment purposes and also for risk management purposes, such as to reduce the duration and interest rate sensitivity of the Fund’s portfolio, and for leveraging purposes. While structured instruments may offer the potential for a favorable rate of return from time to time, they also entail certain risks. Structured instruments may be less liquid than other debt securities, and the price of structured instruments may be more volatile. In some cases, depending on the terms of the embedded index, a structured instrument may provide that the principal and/or interest payments may be adjusted below zero. Structured instruments also may involve significant credit risk and risk of default by the counterparty. Structured instruments may also be illiquid. Like other sophisticated strategies, the Fund’s use of structured instruments may not work as intended. If the value of the embedded index changes in a manner other than that expected by PIMCO, principal and/or interest payments received on the structured instrument may be substantially less than expected. Also, if PIMCO chooses to use structured instruments to reduce the duration of the Fund’s portfolio, this may limit the Fund’s return when having a longer duration would be beneficial (for instance, when interest rates decline).

Rule 144A Securities

The Fund may invest in securities that have not been registered for public sale, but that are eligible for purchase and sale pursuant to Rule 144A under the Securities Act. Rule 144A permits certain qualified institutional buyers, such as the Fund, to trade in privately placed securities that have not been registered for sale under the Securities Act.

Other Investment Companies

The Fund may invest in securities of other open- or closed-end investment companies (including those advised by PIMCO), including without limitation ETFs, to the extent that such investments are consistent with the Fund’s investment objectives, strategies and policies and permissible under the 1940 Act. The Fund may invest in other investment companies (including those advised by PIMCO) to gain broad market, sector exposure or for cash management purposes, including during periods when it has large amounts of uninvested cash (such as the period shortly after the Fund receives the proceeds of the offering of its Common Shares) or when PIMCO believes share prices of other investment companies offer attractive values. The Fund may invest in certain money market funds and/or short-term bond funds (“Central

27 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

Funds”), to the extent permitted by the 1940 Act, the rules thereunder or exemptive relief therefrom. The Central Funds are registered investment companies created for use by certain registered investment companies advised by PIMCO in connection with their cash management activities. The Fund will treat its investments in other investment companies that invest primarily in types of securities in which the Fund may invest directly as investments in such types of securities for purposes of the Fund’s investment policies (e.g., the Fund’s investment in an investment company that invests primarily in debt securities will be treated by the Fund as an investment in a debt security). As a shareholder in an investment company, the Fund would bear its ratable share of that investment company’s expenses and would remain subject to payment of the Fund’s management fees and other expenses with respect to assets so invested. Common Shareholders would therefore be subject to duplicative expenses to the extent the Fund invests in other investment companies. The securities of other investment companies may be leveraged, in which case the NAV and/or market value of the investment company’s shares will be more volatile than unleveraged investments. See “Principal Risks of the Fund—Leverage Risk.”

Regulatory changes adopted by the SEC concerning investments by registered investment companies in the securities of other registered investment companies may, among other things, limit investment flexibility and could affect the Fund’s ability to utilize the Central Funds. This could adversely impact the Fund’s investment strategies and operations. The “Investment Objective and Policies - Regulatory Risk” section in the Statement of Additional Information discusses these changes in further detail.

Repurchase Agreements

The Fund may enter into repurchase agreements, in which the Fund purchases a security from a bank or broker-dealer and the bank or broker-dealer agrees to repurchase the security at the Fund’s cost plus interest within a specified time. If the party agreeing to repurchase should default, the Fund will seek to sell the securities it holds. This could involve transaction costs or delays in addition to a loss on the securities if their value should fall below their repurchase price. Repurchase agreements maturing in more than seven days are considered to be illiquid securities. See “Principal Risks of the Fund—Repurchase Agreements Risk.”

When-Issued, Delayed Delivery and Forward Commitment Transactions

The Fund may purchase securities that it is eligible to purchase on a when-issued basis, may purchase and sell such securities for delayed delivery and may make contracts to purchase such securities for a fixed price at a future date beyond normal settlement time (forward commitments). When-issued transactions, delayed delivery purchases and forward commitments involve a risk of loss if the value of the securities declines prior to the settlement date. This risk is in addition to the risk that the Fund’s other assets will decline in value. Therefore, these transactions may result in a form of leverage and increase the Fund’s overall investment exposure. Typically, no income accrues on

securities the Fund has committed to purchase prior to the time delivery of the securities is made, although the Fund may earn income on securities it has segregated to cover these positions. When the Fund has sold a security on a when-issued, delayed delivery or forward commitment basis, the Fund does not participate in future gains or losses with respect to the security. If the other party to a transaction fails to pay for the securities, the Fund could suffer a loss. Additionally, when selling a security on a when-issued, delayed delivery or forward commitment basis without owning the security, the Fund will incur a loss if the security’s price appreciates in value such that the security’s price is above the agreed-upon price on the settlement date.

Portfolio Turnover

The length of time the Fund has held a particular security is not generally a consideration in investment decisions. A change in the securities held by the Fund is known as “portfolio turnover.” The Fund may engage in frequent and active trading of portfolio securities to achieve its investment objective, particularly during periods of volatile market movements. High portfolio turnover (e.g., over 100%) generally involves correspondingly greater expenses to the Fund, including brokerage commissions or dealer mark-ups and other transaction costs on the sale of securities and reinvestments in other securities. Sales of portfolio securities may also result in realization of taxable capital gains, including short-term capital gains (which are generally treated as ordinary income upon distribution in the form of dividends). The trading costs and tax effects associated with portfolio turnover may adversely affect the Fund’s performance.

Use of Leverage

The amount of leverage that the Fund uses may change, but total leverage is not normally expected to exceed 50% of the Fund’s total assets.

[ ] | Base Prospectus 28

PIMCO Municipal Income Fund

yield curve environment, interest rate trends, market conditions and other factors. The Fund may also determine to decrease the leverage it currently maintains by redeeming its outstanding Preferred Shares or unwinding TOBs and may or may not determine to replace such leverage through other sources. If the Fund determines to add leverage following an offering, it is not possible to predict with accuracy the precise amount of leverage that would be added, in part because it is not possible to predict the number of Common Shares that ultimately will be sold in an offering or series of offerings. To the extent that the Fund does not add additional leverage following an offering, the Fund’s total amount of leverage as a percentage of its total assets will decrease, which could result in a reduction of investment income available for distribution to Common Shareholders.

Under the 1940 Act, the Fund is not permitted to issue new Preferred Shares unless immediately after such issuance the value of the Fund’s total net assets (as defined below) is at least 200% of the liquidation value of the outstanding Preferred Shares and the newly issued Preferred Shares plus the aggregate amount of any senior securities of the Fund representing indebtedness (i.e., such liquidation value plus the aggregate amount of senior securities representing indebtedness may not exceed 50% of the Fund’s total net assets). In addition, the Fund is not permitted to declare any cash dividend or other distribution on its Common Shares unless, at the time of such declaration, the value of the Fund’s total net assets satisfies the above-referenced 200% coverage requirement.

Existing SEC guidance generally prohibits the Fund from engaging in most forms of leverage representing indebtedness other than preferred shares (including the use of TOBs, to the extent that these instruments are not covered as described below) unless immediately after the issuance of the leverage the Fund has satisfied the asset coverage test with respect to senior securities representing indebtedness prescribed by the 1940 Act; that is, the value of the Fund’s total assets less all liabilities and indebtedness not represented by senior securities (for these purposes, “total net assets”) is at least 300% of the senior securities representing indebtedness (effectively limiting the use of leverage through senior securities representing indebtedness to 33 1/3% of the Fund’s total net assets, including assets attributable to such leverage). In addition, the Fund is not permitted to declare any cash dividend or other distribution on its Common Shares unless, at the time of such declaration, this asset coverage test is satisfied. The use of these forms of leverage increases the volatility of the Fund’s investment portfolio and could result in larger losses to Common Shareholders than if these strategies were not used. See “Principal Risks of the Fund—Leverage Risk.” To the extent that the Fund engages in borrowings, it may prepay a portion of the principal amount of the borrowing to the extent necessary in order to maintain the required asset coverage. Failure to maintain certain asset coverage requirements could result in an event of default.

The Fund’s ability to utilize leverage is also limited by asset coverage requirements and other guidelines imposed by rating agencies (currently Moody’s and Fitch) that provide ratings for the Preferred Shares, which are more restrictive than the limitations imposed by the 1940 Act noted above. See “Description of Capital Structure” for more information.

Under the 1940 Act, the Fund is currently not permitted to issue preferred shares unless immediately after such issuance the value of the Fund’s total net assets is at least 200% of the liquidation value of the Fund’s preferred shares plus the aggregate amount of any senior securities of the Fund representing indebtedness (i.e., such liquidation value plus the aggregate amount of senior securities representing indebtedness may not exceed 50% of the Fund’s total net assets). In addition, for so long as the Fund has preferred shares outstanding, the Fund will not be permitted to declare any cash dividend or other distribution on its Common Shares unless, at the time of such declaration, the value of the Fund’s total net assets, after giving effect to such cash dividend or other distribution, satisfies the above-referenced 200% coverage requirement.

Leveraging is a speculative technique and there are special risks and costs involved. The Fund cannot assure you that its use of Preferred Shares and any other forms of leverage (such as TOBs) will be successful or result in a higher yield on your Common Shares. If used, there can be no assurance that the Fund’s leveraging strategies will result in a higher yield on your Common Shares. When leverage is used, the NAV and market price of the Common Shares and the yield to Common Shareholders will be more volatile. See “Principal Risks of the Fund—Leverage Risk.” In addition, dividend, interest and other costs and expenses borne by the Fund with respect to its use of The Fund also may borrow money in order to repurchase its shares or as a temporary measure for extraordinary or emergency purposes, including for the payment of dividends or the settlement of securities transactions which otherwise might require untimely dispositions of portfolio securities held by the Fund.

The Fund also may borrow money in order to repurchase its shares or as a temporary measure for extraordinary or emergency purposes, including for the payment of dividends or the settlement of securities transactions which otherwise might require untimely dispositions of portfolio securities held by the Fund.

Effects of Leverage

The following table is furnished in response to requirements of the SEC. It is designed to illustrate the effects of leverage through the use of senior securities, as that term is defined under Section 18 of the 1940 Act, on Common Share total return, assuming investment portfolio total returns (consisting of income and changes in the value of investments held in the Fund’s portfolio) of -10%, -5%, 0%, 5% and 10%. The table below assumes the Fund’s continued use of Preferred Shares averaged over the year ended December 31, 2021, representing approximately [ ]% of the Fund’s total managed assets, and, although not senior securities under the 1940 Act, the Fund’s use of TOBs averaged over the year ended December 31, 2021, representing approximately [ ]% of the Fund’s total average managed assets. The table below also assumes

29 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

that the Fund will pay dividends on Preferred Shares at an estimated annual effective Preferred Share dividend rate of [ ]% for ARPS and [ ]% for RVMTP (as of June 30, 2022) and interest on TOBs at an estimated annual effective interest expense rate of [ ]% (as of June 30, 2022). Based on such estimates, the annual return that the Fund’s portfolio must experience (net of expenses) in order to cover such costs is [ ]%. The information below does not reflect any Fund’s use of certain other forms of economic leverage achieved through the use of other instruments or transactions not considered to be senior securities under the 1940 Act, such as covered credit default swaps or other derivative instruments.

The assumed investment portfolio returns in the table below are hypothetical figures and are not necessarily indicative of the investment portfolio returns experienced or expected to be experienced by the Fund. Your actual returns may be greater or less than those appearing below. In addition, the actual Preferred Share dividend rate and the actual borrowing expenses associated with TOBs (or other forms of leverage, if any) used by the Fund may vary frequently and may be significantly higher or lower than the rates used for the example below.

Assumed Portfolio Total Return	(10.00)%	(5.00)%	0.00%	5.00%	10.00%
Common Share Total Return	[ ]%	[ ]%	[ ]%	[ ]%	[ ]%

Common Share total return is composed of two elements—the Common Share dividends paid by the Fund (the amount of which is largely determined by the net investment income of the Fund after paying dividends on Preferred Shares and expenses on any forms of leverage outstanding, including TOBs) and gains or losses on the value of the securities and other instruments the Fund owns. As required by SEC rules, the table assumes that the Fund is more likely to suffer capital losses than to enjoy capital appreciation. For example, to assume a portfolio total return of 0%, the Fund must assume that the income it receives on its investments is entirely offset by losses in the value of those investments. This table reflects hypothetical performance of the Fund’s portfolio and not the actual performance of the Fund’s Common Shares, the value of which is determined by market forces and other factors.

Should the Fund elect to add additional leverage to its portfolio following an offering, any benefits of such additional leverage cannot be fully achieved until the proceeds resulting from the use of such leverage have been received by the Fund and invested in accordance with the Fund’s investment objective and policies. As noted above, the Fund’s willingness to use additional leverage, and the extent to which leverage is used at any time, will depend on many factors, including, among other things, PIMCO’s assessment of the yield curve environment, interest rate trends, market conditions and other factors.

Principal Risks of the Fund

The Fund is subject to the principal risks noted below, whether through the Fund’s direct investments or derivatives positions.

Market Discount Risk

Market Risk

[ ] | Base Prospectus 30

PIMCO Municipal Income Fund

shutdowns may affect investor and consumer confidence and may adversely impact financial markets and the broader economy, perhaps suddenly and to a significant degree. Governmental and quasi-governmental authorities and regulators throughout the world have previously responded to serious economic disruptions with a variety of significant fiscal and monetary policy changes, including but not limited to, direct capital infusions into companies, new monetary programs and dramatically lower interest rates. An unexpected or sudden reversal of these policies, or the ineffectiveness of these policies, could increase volatility in securities markets, which could adversely affect the Fund’s investments. Any market disruptions could also prevent the Fund from executing advantageous investment decisions in a timely manner. Funds that have focused their investments in a region enduring geopolitical market disruption, it will face higher risks of loss. Thus, investors should closely monitor current market conditions to determine whether the Fund meets their individual financial needs and tolerance for risk.

Current market conditions may pose heightened risks with respect to the Fund’s investment in fixed income securities.. As such, fixed income securities markets may experience heightened levels of interest rate, volatility and liquidity risk. Any interest rate increases in the future could cause the value of any Fund, such as the Fund, that invests in fixed income securities to decrease.

Exchanges and securities markets may close early, close late or issue trading halts on specific securities, which may result in, among other things, the Fund being unable to buy or sell certain securities or financial instruments at an advantageous time or accurately price its portfolio investments.

Municipal Bond Risk

proceeds of a special excise or other specific revenue source, there is no guarantee that the particular project will generate enough revenue to pay its obligations, in which case the Fund’s performance may be adversely affected.

Municipal securities are also subject to interest rate, credit, and liquidity risk, which are discussed generally elsewhere in this section, and elaborated upon below with respect to municipal bonds.

This subjects the Fund to credit risk in that the municipal issuer may be fiscally unstable or exposed to large liabilities that could impair its ability to honor its obligations. Municipal issuers with significant debt service requirements, in the near-to mid-term; unrated issuers and those with less capital and liquidity to absorb additional expenses may be most at risk. To the extent the Fund invests in lower quality or high yield municipal securities, it may be more sensitive to the adverse credit events in the municipal market. The treatment of municipalities in bankruptcy is more uncertain, and potentially more adverse to debt holders, than for corporate issues.

31 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

municipality’s ability to raise tax revenue and maintain a fiscally sound budget. The timely payments may also be influenced by any unfunded pension liabilities or other post-employee benefit plan (OPEB) liabilities.

Revenue bonds are secured by special tax revenues or other revenue sources. If the specified revenues do not materialize, then the bonds may not be repaid.

Municipal Project-Specific Risk

U.S. Government Securities Risk

are supported only by the credit of the agency, instrumentality or corporation. Although legislation has been enacted to support certain government sponsored entities, including the FHLBs, FHLMC and FNMA, there is no assurance that the obligations of such entities will be satisfied in full, or that such obligations will not decrease in value or default. It is difficult, if not impossible, to predict the future political, regulatory or economic changes that could impact the government sponsored entities and the values of their related securities or obligations. In addition, certain governmental entities, including FNMA and FHLMC, have been subject to regulatory scrutiny regarding their accounting policies and practices and other concerns that may result in legislation, changes in regulatory oversight and/or other consequences that could adversely affect the credit quality, availability or investment character of securities issued by these entities. Yields available from U.S. government debt securities are generally lower than the yields available from other debt securities. The values of U.S. government securities change as interest rates fluctuate.

Asset Allocation Risk

The Fund’s investment performance depends upon how its assets are allocated and reallocated. A principal risk of investing in the Fund is that PIMCO may make less than optimal or poor asset allocation decisions. PIMCO employs an active approach to allocation among multiple fixed-income sectors, but there is no guarantee that such allocation techniques will produce the desired results. It is possible that PIMCO will focus on an investment that performs poorly or underperforms other investments under various market conditions. You could lose money on your investment in the Fund as a result of these allocation decisions.

Management Risk

[ ] | Base Prospectus 32

PIMCO Municipal Income Fund

restrictions, policies or developments may affect the investment techniques available to PIMCO and each individual portfolio manager in connection with managing the Fund and may also adversely affect the ability of the Fund to achieve its investment objective. There also can be no assurance that all of the personnel of PIMCO will continue to be associated with PIMCO for any length of time. The loss of the services of one or more key employees of PIMCO could have an adverse impact on the Fund’s ability to realize its investment objective.

In addition, the Fund may rely on various third-party sources to calculate its NAV. As a result, the Fund is subject to certain operational risks associated with reliance on service providers and service providers’ data sources. In particular, errors or systems failures and other technological issues may adversely impact the Fund’s calculations of its NAV, and such NAV calculation issues may result in inaccurately calculated NAV, delays in NAV calculation and/or the inability to calculate NAVs over extended periods. The Fund may be unable to recover any losses associated with such failures.

Issuer Risk

Interest Rate Risk

Interest rate risk is the risk that fixed income securities and other instruments in the Fund’s portfolio will decline in value because of a change in interest rates. As nominal interest rates rise, the value of certain fixed income securities held by the Fund is likely to decrease. A nominal interest rate can be described as the sum of a real interest rate and an expected inflation rate. Interest rate changes can be sudden and unpredictable, and the Fund may lose money as a result of movements in interest rates. The Fund may not be able to effectively hedge against changes in interest rates or may choose not to do so for cost or other reasons.

Fixed income securities with longer durations tend to be more sensitive to changes in interest rates, usually making them more volatile. Duration is a measure used to determine the sensitivity of a security’s price to changes in interest rates that incorporates a security’s yield, coupon, final maturity and call features, among other characteristics. Duration is useful primarily as a measure of the sensitivity of a fixed income security’s market price to interest rate (i.e., yield) movements. All other

things remaining equal, for each one percentage point increase in interest rates, the value of a portfolio of fixed income investments would generally be expected to decline by one percent for every year of the portfolio’s average duration above zero. For example, the value of a portfolio of fixed income securities with an average duration of fourteen years would generally be expected to decline by approximately 14% if interest rates rose by one percentage point.

Variable and floating rate securities may decline in value if their interest rates do not rise as much, or as quickly, as interest rates in general. Conversely, floating rate securities will not generally increase in value if interest rates decline. Inverse floating rate securities may decrease in value if interest rates increase. Inverse floating rate securities may also exhibit greater price volatility than a fixed rate obligation with similar credit quality. When the Fund holds variable or floating rate securities, a decrease (or, in the case of inverse floating rate securities, an increase) in market interest rates will adversely affect the income received from such securities and the NAV of the Fund’s shares.

During periods of very low or negative interest rates, the Fund may be unable to maintain positive returns. Very low or negative interest rates may magnify interest rate risk. Changing interest rates, including rates that fall below zero, may have unpredictable effects on markets, may result in heightened market volatility and may detract from Fund performance to the extent the Fund is exposed to such interest rates.

Measures such as average duration may not accurately reflect the true interest rate sensitivity of the Fund. This is especially the case if the Fund consists of securities with widely varying durations. Therefore, if the Fund has an average duration that suggests a certain level of interest rate risk, the Fund may in fact be subject to greater interest rate risk than the average would suggest. This risk is greater to the extent the Fund uses leverage or derivatives.

Convexity is an additional measure used to understand a security’s or Fund’s interest rate sensitivity. Convexity measures the rate of change of duration in response to changes in interest rates. With respect to a security’s price, a larger convexity (positive or negative) may imply more dramatic price changes in response to changing interest rates. Convexity may be positive or negative. Negative convexity implies that interest rate increases result in increased duration, meaning increased sensitivity in prices in response to rising interest rates. Thus, securities with negative convexity, which may include bonds with traditional call features and certain mortgage-backed securities, may experience greater losses in periods of rising interest rates. Accordingly, if the Fund holds such securities, the Fund may be subject to a greater risk of losses in periods of rising interest rates.

Rising interest rates may result in periods of volatility and a decline in value of the Fund’s fixed income investments. Further, while U.S. bond markets have steadily grown over the past three decades, dealer “market making” ability has remained relatively stagnant. As a result, dealer inventories of certain types of bonds and similar instruments, which provide a core indication of the ability of financial intermediaries to “make markets,” are at or near historic lows in relation to market size. Because market makers provide stability to a market through their intermediary services, a significant reduction in dealer inventories could

33 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

potentially lead to decreased liquidity and increased volatility in the fixed income markets. Such issues may be exacerbated during periods of economic uncertainty. All of these factors, collectively and/or individually, could cause the Fund to lose value.

Credit Risk

The Fund could lose money if the issuer or guarantor of a fixed income security, or the counterparty to a derivatives contract, repurchase agreement or a loan of portfolio securities, is unable or unwilling, or is perceived as unable or unwilling, to make timely principal and/or interest payments or to otherwise honor its obligations. The downgrade of the credit of a security held by the Fund may decrease its value. Measures such as average credit quality may not accurately reflect the true credit risk of the Fund. This is especially the case if the Fund consists of securities with widely varying credit ratings. This risk is greater to the extent the Fund uses leverage or derivatives. Municipal bonds are subject to the risk that litigation, legislation or other political events, local business or economic conditions, or the bankruptcy of the issuer could have a significant effect on an issuer’s ability to make payments of principal and/or interest.

Mortgage-Related and Other Asset-Backed Instruments Risk

The mortgage-related assets in which the Fund may invest include, but are not limited to, any security, instrument or other asset that is related to U.S. or non-U.S. mortgages, including those issued by private originators or issuers, or issued or guaranteed as to principal or interest by the U.S. government or its agencies or instrumentalities or by non-U.S. governments or authorities, such as, without limitation, assets representing interests in, collateralized or backed by, or whose values are determined in whole or in part by reference to any number of mortgages or pools of mortgages or the payment experience of such mortgages or pools of mortgages, including REMICs, which could include Re-REMICs, mortgage pass-through securities, inverse floaters, CMOs, CLOs, multiclass pass-through securities, private mortgage pass-through securities, stripped mortgage securities (generally interest-only and principal-only securities), mortgage-related asset backed securities and mortgage-related loans (including through participations, assignments, originations and whole loans), including commercial and residential mortgage loans. Exposures to mortgage-related assets through derivatives or other financial instruments will be considered investments in mortgage-related assets.

The Fund may also invest in other types of ABS, including CDOs, CBOs and CLOs and other similarly structured securities See “The Fund’s Investment Objective and Strategies-Portfolio Contents and Other Information-Mortgage-Related and Other Asset-Backed Instruments” in this prospectus and “Investment Objective and Policies-Mortgage-Related and Other Asset-Backed Instruments” in the Statement of Additional Information for a description of the various mortgage-related and other asset-backed instruments in which the Fund may invest and their related risks.

Mortgage-related and other asset-backed instruments represent interests in “pools” of mortgages or other assets such as consumer loans or receivables held in trust and often involve risks that are different from or possibly more acute than risks associated with other types of debt instruments.

Generally, rising interest rates tend to extend the duration of fixed rate mortgage-related assets, making them more sensitive to changes in interest rates. As a result, in a period of rising interest rates, the Fund may exhibit additional volatility since individual mortgage holders are less likely to exercise prepayment options, thereby putting additional downward pressure on the value of these securities and potentially causing the Fund to lose money. This is known as extension risk. Mortgage-backed securities can be highly sensitive to rising interest rates, such that even small movements can cause the Fund to lose value. Mortgage-backed securities, and in particular those not backed by a government guarantee, are subject to credit risk. When interest rates decline, borrowers may pay off their mortgages sooner than expected. This can reduce the returns of the Fund because the Fund may have to reinvest that money at the lower prevailing interest rates. The Fund’s investments in other asset-backed instruments are subject to risks similar to those associated with mortgage-related assets, as well as additional risks associated with the nature of the assets and the servicing of those assets. Payment of principal and interest on asset-backed instruments may be largely dependent upon the cash flows generated by the assets backing the instruments, and asset-backed instruments may not have the benefit of any security interest in the related assets.

Subordinate mortgage-backed or asset-backed instruments are paid interest only to the extent that there are funds available to make payments. To the extent the collateral pool includes a large percentage of delinquent loans, there is a risk that interest payments on subordinate mortgage-backed or asset-backed instruments will not be fully paid.

There are multiple tranches of mortgage-backed and asset-backed instruments, offering investors various maturity and credit risk characteristics. Tranches are categorized as senior, mezzanine, and subordinated/equity or “first loss,” according to their degree of risk. The most senior tranche of a mortgage-backed or asset-backed instrument has the greatest collateralization and pays the lowest interest rate. If there are defaults or the collateral otherwise underperforms, scheduled payments to senior tranches take precedence over those of mezzanine tranches, and scheduled payments to mezzanine tranches take precedence over those to subordinated/equity tranches. Lower tranches represent lower degrees of credit quality and pay higher interest rates intended to compensate for the attendant risks. The return on the lower tranches is especially sensitive to the rate of defaults in the collateral pool. The lowest tranche (i.e., the “equity” or “residual” tranche) specifically receives the residual interest payments (i.e., money that is left over after the higher tranches have been paid and expenses of the issuing entities have been paid) rather than a fixed interest rate. The Fund may also invest in the residual or equity tranches of mortgage-related and other asset-backed instruments, which may be

[ ] | Base Prospectus 34

PIMCO Municipal Income Fund

referred to as subordinate mortgage-backed or asset-backed instruments and interest-only mortgage-backed or asset-backed instruments. The Fund expects that investments in subordinate mortgage-backed and other asset-backed instruments will be subject to risks arising from delinquencies and foreclosures, thereby exposing its investment portfolio to potential losses. Subordinate securities of mortgage-backed and other asset-backed instruments are also subject to greater credit risk than those mortgage-backed or other asset-backed instruments that are more highly rated.

Mortgage-Related Derivative Instruments Risk

Derivative mortgage-backed securities (such as principal-only (“POs”), interest-only (“IOs”) or inverse floating rate securities) are particularly exposed to call and extension risks. Small changes in mortgage prepayments can significantly impact the cash flows and the market value of these derivative instruments. In general, the risk of faster than anticipated prepayments adversely affects IOs, super floaters and premium priced mortgage- backed securities. The risk of slower than anticipated prepayments generally affects POs, floating-rate securities subject to interest rate caps, support tranches and discount priced mortgage-backed securities. In addition, particular derivative instruments may be leveraged such that their exposure (i.e., price sensitivity) to interest rate and/or prepayment risk is magnified. Mortgage-related derivative instruments involve risks associated with mortgage-related and other asset-backed instruments, privately-issued mortgage-related securities, the mortgage market, the real estate industry, derivatives and credit default swaps. See “Mortgage-Related

and Other Asset-Backed Instruments Risk,” “Privately-Issued Mortgage-Related Securities Risk,” “Derivatives Risk,” and “Credit Default Swaps Risk.”

High Yield Securities Risk

Issuers of high yield securities may have the right to “call” or redeem the issue prior to maturity, which may result in the Fund having to reinvest the proceeds in other high yield securities or similar instruments that may pay lower interest rates. The Fund may also be subject to greater levels of liquidity risk than funds that do not invest in high yield securities. Consequently, transactions in high yield securities may involve greater costs than transactions in more actively traded securities. To the extent that the Fund invests in high yield securities and unrated securities of similar credit quality (commonly known as “high yield securities” or “junk bonds”), the Fund may be subject to greater levels of credit risk, call risk and liquidity risk than funds that do not invest in such securities, which could have a negative effect on the NAV and market price of the Fund’s Common Shares or Common Share dividends. These securities are considered predominantly speculative with respect to an issuer’s continuing ability to make principal and interest payments, and may be more volatile than other types of securities. An economic downturn or individual corporate developments could adversely affect the market for these securities and reduce the Fund’s ability to sell these securities at an advantageous time or price. The Fund may purchase distressed securities that are in default or the issuers of which are in bankruptcy, which involve heightened risks. Issuers of high yield securities may have the right to “call” or redeem the issue prior to maturity, which may result in the Fund having to reinvest the proceeds in other high yield securities or similar instruments that may pay lower interest rates. The Fund may also be subject to greater levels of liquidity risk than funds that do not invest in high yield securities. Consequently, transactions in high yield securities may

35 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

involve greater costs than transactions in more actively traded securities. These factors may result in the Fund being unable to realize full value for these securities and/or may result in the Fund not receiving the proceeds from a sale of a high yield security for an extended period after such sale, each of which could result in losses to the Fund. Because of the risks involved in investing in high yield securities, an investment in the Fund should be considered speculative.

In general, lower rated debt securities carry a greater degree of risk that the issuer will lose its ability to make interest and principal payments, which could have a negative effect on the Fund. Securities of below investment grade quality are regarded as having predominantly speculative characteristics with respect to capacity to pay interest and repay principal and are commonly referred to as “high yield” securities or “junk bonds.” High yield securities involve a greater risk of default and their prices are generally more volatile and sensitive to actual or perceived negative developments. Debt securities in the lowest investment grade category also may be considered to possess some speculative characteristics by certain rating agencies. The Fund may purchase stressed or distressed securities that are in default or the issuers of which are in bankruptcy, which involve heightened risks.

An economic downturn could severely affect the ability of issuers (particularly those that are highly leveraged) to service or repay their debt obligations. Lower-rated securities are generally less liquid than higher-rated securities, which may have an adverse effect on the Fund’s ability to dispose of them. For example, under adverse market or economic conditions, the secondary market for below investment grade securities could contract further, independent of any specific adverse changes in the condition of a particular issuer, and certain securities in the Fund’s portfolio may become illiquid or less liquid. As a result, the Fund could find it more difficult to sell these securities or may be able to sell these securities only at prices lower than if such securities were widely traded. To the extent the Fund focuses on below investment grade debt obligations, PIMCO’s capabilities in analyzing credit quality and associated risks will be particularly important, and there can be no assurance that PIMCO will be successful in this regard. Due to the risks involved in investing in high yield securities, an investment in the Fund should be considered speculative.

The Fund’s credit quality policies apply only at the time a security is purchased, and the Fund is not required to dispose of a security in the event that a rating agency or PIMCO downgrades its assessment of the credit characteristics of a particular issue. Analysis of creditworthiness may be more complex for issuers of high yield securities than for issuers of higher quality debt securities.

Reinvestment Risk

purchase lower yielding securities to achieve greater portfolio diversification, because the portfolio managers believe the current holdings are overvalued or for other investment-related reasons. A decline in income received by the Fund from its investments is likely to have a negative effect on dividend levels and the market price, NAV and/or overall return of the Common Shares.

Securities Lending Risk

Call Risk

U.S. Government Securities Risk

Certain U.S. government securities, such as U.S. Treasury bills, notes, bonds and mortgage-related securities guaranteed by the GNMA, are supported by the full faith and credit of the United States; others, such as those of the FHLBs or the FHLMC, are supported by the right of the issuer to borrow from the U.S. Treasury; others, such as those of the FNMA, are supported by the discretionary authority of the U.S. government to purchase the agency’s obligations; and still others are supported only by the credit of the agency, instrumentality or corporation. Although legislation has been enacted to support certain government sponsored entities, including the FHLBs, FHLMC and FNMA, there is no assurance that the obligations of such entities will be satisfied in full, or that such obligations will not decrease in value or default. It is difficult, if not impossible, to predict the future political, regulatory or economic changes that could impact the government sponsored entities and the values of their related securities or obligations. In addition, certain governmental entities, including FNMA and FHLMC, have been subject to regulatory scrutiny regarding their

[ ] | Base Prospectus 36

PIMCO Municipal Income Fund

accounting policies and practices and other concerns that may result in legislation, changes in regulatory oversight and/or other consequences that could adversely affect the credit quality, availability or investment character of securities issued by these entities. Yields available from U.S. government debt securities are generally lower than the yields available from other debt securities. The values of U.S. government securities change as interest rates fluctuate.

California State-Specific Risk

New York State-Specific Risk

The Fund may be affected significantly by economic, regulatory or political developments affecting the ability of New York issuers to pay interest or repay principal. Certain issuers of New York municipal bonds have experienced serious financial difficulties in the past and reoccurrence of these difficulties may impair the ability of certain New York issuers to pay principal or interest on their obligations. Provisions of the New York Constitution and State statutes which limit the taxing and spending authority of New York governmental entities may impair the ability of New York issuers to pay principal and/or interest on their obligations. While New York’s economy is broad, it does have major concentrations in certain industries, such as financial services, and may be sensitive to economic problems affecting those industries. Future New York political and economic developments, constitutional amendments, legislative measures, executive orders, administrative regulations, litigation and voter initiatives could have an adverse effect on the debt obligations of New York issuers.

Puerto Rico-Specific Risk

Commonwealth laws, including a federally-appointed oversight board to oversee the Commonwealth’s financial operations, which limit the taxing and spending authority of Puerto Rico governmental entities may impair the ability of Puerto Rico issuers to pay principal and/or interest on their obligations. While Puerto Rico’s economy is broad, it does have major concentrations in certain industries, such as manufacturing and service, and may be sensitive to economic problems affecting those industries. Future Puerto Rico political and economic developments, constitutional amendments, legislative measures, executive orders, administrative regulations, litigation, debt restructuring, and voter initiatives could have an adverse effect on the debt obligations of Puerto Rico issuers.

Valuation Risk

Certain securities in which the Fund invests may be less liquid and more difficult to value than other types of securities. When market quotations or pricing service prices are not readily available or are deemed to be unreliable, the Fund values its investments at fair value as determined in good faith pursuant to policies and procedures approved by the Board. Fair value pricing may require subjective determinations about the value of a security or other asset. As a result, there can be no assurance that fair value pricing will result in adjustments to the prices of securities or other assets or that fair value pricing will reflect actual market value, and it is possible that the fair value determined for a security or other asset will be materially different from quoted or published prices, from the prices used by others for the same security or other asset and/or from the value that actually could be or is realized upon the sale of that security or other asset.

Leverage Risk

The Fund’s use of leverage (as described under “Use of Leverage” in the body of this prospectus) creates the opportunity for increased Common Share net income, but also creates special risks for Common Shareholders. To the extent used, there is no assurance that the Fund’s leveraging strategies will be successful. Leverage is a speculative technique that may expose the Fund to greater risk and increased costs. The Fund’s assets attributable to any outstanding Preferred Shares or the net proceeds that the Fund obtains from its use of TOBs, derivatives or other forms of leverage, if any, will be invested in accordance with the Fund’s investment objective and policies as described in this prospectus. Dividends payable with respect to Preferred Shares outstanding and interest expense payable by the Fund with respect to any TOBs, derivatives and other forms of leverage will generally be based on shorter-term interest rates that would be periodically reset. If shorter-term interest rates rise relative to the rate of return on the Fund’s portfolio, the interest and other costs to the Fund of leverage (including interest expenses on TOBs and the dividend rate on any outstanding Preferred Shares s, including the Preferred Shareholder Gross-Up (as defined below)) could exceed the rate of return on the debt obligations and other investments held by the Fund, thereby reducing return to Common Shareholders. In addition, fees and expenses of any form of leverage used by the Fund will be borne entirely by the Common Shareholders (and not by preferred shareholders) and

37 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

will reduce the investment return of the Common Shares. Therefore, there can be no assurance that the Fund’s use of leverage will result in a higher yield on the Common Shares, and it may result in losses. In addition, Preferred Shares issued by the Fund pay cumulative dividends, which may tend to increase leverage risk. Leverage creates several major types of risks for Common Shareholders, including:

◾

the likelihood of greater volatility of NAV and market price of Common Shares, and of the investment return to Common Shareholders, than a comparable portfolio without leverage;

◾

In addition, the counterparties to the Fund’s leveraging transactions and preferred shareholders of the Fund will have priority of payment over the Fund’s Common Shareholders.

shareholders may have interests that differ from those of Common Shareholders, and may at times have disproportionate influence over the Fund’s affairs.

Short Exposure Risk

The Fund’s short sales, if any, are subject to special risks. A short sale involves the sale by the Fund of a security that it does not own with the hope of purchasing the same security at a later date at a lower price. The Fund may also enter into a short position through a forward commitment or a short derivative position through a futures contract or swap agreement. If the price of the security or derivative has increased during this time, then the Fund will incur a loss equal to the increase in price from the time that the short sale was entered into plus any transaction costs (i.e., premiums and interest) paid to the broker-dealer to borrow securities. Therefore, short sales involve the risk that losses may be exaggerated, potentially losing more money than the actual cost of the investment. By contrast, a loss on a long position arises from decreases in the value of the security and is limited by the fact that a security’s value cannot decrease below zero. By investing the proceeds received from selling securities short, the Fund could be deemed to be employing a form of leverage, which creates special risks. The use of leverage may increase the Fund’s exposure to long security positions and make any change in the Fund’s NAV greater than it would be without the use of leverage. This could result in increased volatility of returns. There is no guarantee that any leveraging strategy the Fund employs will be successful during any period in which it is employed.

In times of unusual or adverse market, economic, regulatory or political conditions, the Fund may not be able, fully or partially, to implement its short selling strategy. Periods of unusual or adverse market, economic, regulatory or political conditions generally may exist for long periods of time. Also, there is the risk that the third party to the short sale will not fulfill its contractual obligations, causing a loss to the Fund.

Derivatives Risk

The use of derivative instruments involves risks different from, and possibly greater than, the risks associated with investing directly in securities and other traditional investments.

Derivatives are subject to a number of risks, such as liquidity risk (which may be heightened for highly-customized derivatives), interest rate risk, market risk, credit risk, leveraging risk, counterparty risk, tax risk and management risk, as well as risks arising from changes in applicable requirements. They also involve the risk of mispricing, the risk of unfavorable or ambiguous documentation and the risk that changes in the value of a derivative may not correlate perfectly with the underlying asset, rate or index. If the Fund invests in a derivative instrument, the Fund could lose more than the amount invested and derivatives may

[ ] | Base Prospectus 38

PIMCO Municipal Income Fund

increase the volatility of the Fund, especially in unusual or extreme market conditions. Also, suitable derivative transactions may not be available in all circumstances and there can be no assurance that the Fund will engage in these transactions to reduce exposure to other risks when that would be beneficial or that, if used, such strategies will be successful. The Fund’s use of derivatives may increase or accelerate the amount of taxes payable by Common Shareholders.

Over-the-counter (“OTC”) derivatives are also subject to the risk that a counterparty to the transaction will not fulfill its contractual obligations to the other party, as many of the protections afforded to centrally-cleared derivative transactions might not be available for OTC derivative transactions. For derivatives traded on an exchange or through a central counterparty, credit risk resides with the Fund’s clearing broker, or the clearinghouse, rather than with a counterparty in an OTC derivative transaction. The primary credit risk on derivatives that are exchange-traded or traded through a central clearing counterparty resides with the Fund’s clearing broker, or the clearinghouse. Participation in the markets for derivative instruments involves investment risks and transaction costs to which the Fund may not be subject absent the use of these strategies. The skills needed to successfully execute derivative strategies may be different from those needed for other types of transactions. If the Fund incorrectly forecasts the value and/or creditworthiness of securities, currencies, interest rates, counterparties or other economic factors involved in a derivative transaction, the Fund might have been in a better position if the Fund had not entered into such derivative transaction. In evaluating the risks and contractual obligations associated with particular derivative instruments, it is important to consider that certain derivative transactions may be modified or terminated only by mutual consent of the Fund and its counterparty.

Therefore, it may not be possible for the Fund to modify, terminate, or offset the Fund’s obligations or the Fund’s exposure to the risks associated with a derivative transaction prior to its scheduled termination or maturity date, which may create a possibility of increased volatility and/or decreased liquidity to the Fund.

Because the markets for certain derivative instruments (including markets located in foreign countries) are relatively new and still developing, appropriate derivative transactions may not be available in all circumstances for risk management or other purposes. Upon the expiration of a particular contract, the Fund may wish to retain the Fund’s position in the derivative instrument by entering into a similar contract, but may be unable to do so if the counterparty to the original contract is unwilling to enter into the new contract and no other appropriate counterparty can be found. When such markets are unavailable, the Fund will be subject to increased liquidity and investment risk.

The Fund may enter into opposite sides of interest rate swap and other derivatives for the principal purpose of generating distributable gains on the one side (characterized as ordinary income for tax purposes) that are not part of the Fund’s duration or yield curve management strategies (“paired swap transactions”), and with a substantial possibility that the Fund will experience a corresponding capital loss

and decline in NAV with respect to the opposite side transaction (to the extent it does not have corresponding offsetting capital gains). Consequently, Common Shareholders may receive distributions and owe tax on amounts that are effectively a taxable return of the shareholder’s investment in the Fund, at a time when their investment in the Fund has declined in value, which tax may be at ordinary income rates. The tax treatment of certain derivatives in which the Fund invests may be unclear and thus subject to recharacterization. Any recharacterization of payments made or received by the Fund pursuant to derivatives potentially could affect the amount, timing or character of Fund distributions. In addition, the tax treatment of such investment strategies may be changed by regulation or otherwise.

When a derivative is used as a hedge against a position that the Fund holds, any loss generated by the derivative generally should be substantially offset by gains on the hedged investment, and vice versa. Although hedging can reduce or eliminate losses, it can also reduce or eliminate gains. Hedges are sometimes subject to imperfect matching between the derivative and the underlying instrument, and there can be no assurance that the Fund’s hedging transactions will be effective. In such case, the Fund may lose money. The regulation of the derivatives markets has increased over the past several years, and additional future regulation of the derivatives markets may make derivatives more costly, may limit the availability or reduce the liquidity of derivatives or may otherwise adversely affect the value or performance of derivatives. Any such adverse future developments could impair the effectiveness or raise the costs of the Fund’s derivative transactions, impede the employment of the Fund’s derivatives strategies, or adversely affect the Fund’s performance and cause the Fund to lose value.

Counterparty Risk

The Fund will be subject to credit risk with respect to the counterparties to the derivative contracts and other instruments entered into by the Fund or held by special purpose or structured vehicles in which the Fund invests. In the event that the Fund enters into a derivative transaction with a counterparty that subsequently becomes insolvent or becomes the subject of a bankruptcy case, the derivative transaction may be terminated in accordance with its terms and the Fund’s ability to realize its rights under the derivative instrument and its ability to distribute the proceeds could be adversely affected. If a counterparty becomes bankrupt or otherwise fails to perform its obligations under a derivative contract due to financial difficulties, the Fund may experience significant delays in obtaining any recovery (including recovery of any collateral it has provided to the counterparty) in a dissolution, assignment for the benefit of creditors, liquidation, winding-up, bankruptcy or other analogous proceeding. In addition, in the event of the insolvency of a counterparty to a derivative transaction, the derivative transaction would typically be terminated at its fair market value. If the Fund is owed this fair market value in the termination of the derivative transaction and its claim is unsecured, the Fund will be treated as a general creditor of such counterparty and will not have any claim with respect to any underlying security or asset. The Fund may obtain only a limited recovery or may obtain no recovery in such circumstances. While the Fund may seek to manage its counterparty risk by transacting with a

39 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

number of counterparties, concerns about the solvency of, or a default by, one large market participant could lead to significant impairment of liquidity and other adverse consequences for other counterparties.

Additional Risks Associated with the Fund’s Preferred Shares

Although the Fund’s ARPS ordinarily would pay dividends at rates set at periodic auctions, the weekly auctions for the ARPS (and auctions for similar preferred shares issued by closed-end funds in the U.S.) have failed since 2008. The dividend rates on the ARPS since that time have been paid, and the Fund expects that they will continue to be paid for the foreseeable future, at the “maximum applicable rate.”

may make such guidelines substantially more restrictive or otherwise result in downgrades, which could further negatively affect the Fund’s investment performance.

Confidential Information Access Risk

Private Placements and Restricted Securities Risk

[ ] | Base Prospectus 40

PIMCO Municipal Income Fund

subject to strict restrictions on resale, and there may be no liquid secondary market or ready purchaser for such securities. See “Principal Risks of the Fund – Liquidity Risk.” Therefore, the Fund may be unable to dispose of such securities when it desires to do so, or at the most favorable time or price. Private placements may also raise valuation risks. Restricted securities are often purchased at a discount from the market price of unrestricted securities of the same issuer reflecting the fact that such securities may not be readily marketable without some time delay. Such securities are often more difficult to value and the sale of such securities often requires more time and results in higher brokerage charges or dealer discounts and other selling expenses than does the sale of securities trading on national securities exchanges or in the over-the-counter markets. Until the Fund can sell such securities into the public markets, its holdings may be less liquid and any sales will need to be made pursuant to an exemption under the Securities Act.

Inflation/Deflation Risk

Regulatory Changes Risk

Financial entities, such as investment companies and investment advisers, are generally subject to extensive government regulation and intervention. Government regulation and/or intervention may change the way the Fund is regulated, affect the expenses incurred directly by the Fund and the value of its investments, and limit and /or preclude the Fund’s ability to achieve its investment objective. Government regulation may change frequently and may have significant adverse consequences. The Fund and the Investment Manager have historically been eligible for exemptions from certain regulations. However, there is no assurance that the Fund and the Investment Manager will continue to be eligible for such exemptions. Actions by governmental entities may also impact certain instruments in which the Fund invests.

Moreover, government regulation may have unpredictable and unintended effects. Legislative or regulatory actions to address perceived liquidity or other issues in fixed income markets generally, or in particular markets such as the municipal securities market, may alter or impair the Fund’s ability to pursue its investment objective or utilize certain investment strategies and techniques.

Current rules related to credit risk retention requirements for ABS may increase the cost to originators, securitizers and, in certain cases, asset managers of securitization vehicles in which the Fund may invest. The impact of the risk retention rules on the securitization markets is uncertain. These requirements may increase the costs to originators, securitizers, and, in certain cases, collateral managers of securitization

vehicles in which the Fund may invest, which costs could be passed along to the Fund as an investor in such vehicles. In addition, the costs imposed by the risk retention rules on originators, securitizers and/or collateral managers may result in a reduction of the number of new offerings of ABS and thus in fewer investment opportunities for the Fund. A reduction in the number of new securitizations could also reduce liquidity in the markets for certain types of financial assets, which in turn could negatively affect the returns on the Fund’s investment.

Regulatory Risk - London Interbank Offered Rate (“LIBOR”)

The Fund’s investments (including, but not limited to, repurchase agreements, collateralized loan obligations and mortgage-backed securities), payment obligations and financing terms may rely in some fashion on the London Interbank Offered Rate (“LIBOR”). LIBOR is an average interest rate, determined by the ICE Benchmark Administration that banks charge one another for the use of short-term money. ,On July 27, 2017, the Chief Executive of the FCA announced that after 2021 it would cease its active encouragement of banks to provide the quotations needed to sustain LIBOR due to the absence of an active market for interbank unsecured lending and other reasons. On March 5, 2021, the FCA publicly announced that all U.S. Dollar LIBOR settings will either cease to be provided by any administrator or will no longer be representative (i) immediately after December 31, 2021 for one-week and two-month U.S. Dollar LIBOR settings and (ii) immediately after June 30, 2023 for the remaining U.S. Dollar LIBOR settings. As of January 1, 2022, as a result of supervisory guidance from U.S. regulators, some U.S. regulated entities have ceased entering into new LIBOR contracts with limited exceptions. While publication of the one-, three- and six- month Sterling and Japanese yen LIBOR settings will continue at least through calendar year 2022 on the basis of a changed methodology (known as “synthetic LIBOR”), these rates have been designated by the FCA as unrepresentative of the underlying market they seek to measure and are solely available for use in legacy transactions. Certain bank-sponsored committees in other jurisdictions, including Europe, the United Kingdom, Japan and Switzerland, have selected alternative reference rates denominated in other currencies. Although the transition process away from LIBOR has become increasingly well-defined in advance of the anticipated discontinuation date, there remains uncertainty regarding the future utilization of LIBOR and the nature of any replacement rate (e.g., the Secured Overnight Financing Rate, which is intended to replace U.S. dollar LIBOR and measures the cost of overnight borrowings through repurchase agreement transactions collateralized with U.S. Treasury securities). Any potential effects of the transition away from LIBOR on the Fund or on certain instruments in which the Fund invests can be difficult to ascertain, and they may vary depending on factors that include, but are not limited to: (i) existing fallback or termination provisions in individual contracts and (ii) whether, how, and when industry participants develop and adopt new reference rates and fallbacks for both legacy and new products and instruments. For example, certain of the Fund’s investments may involve individual contracts that have no existing fallback provision or language that contemplates the discontinuation of LIBOR, and those investments could experience increased volatility or

41 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

illiquidity as a result of the transition process. In addition, interest rate provisions included in such contracts, or in contracts or other arrangements entered into by the Fund, may need to be renegotiated. On March 15, 2022, the Adjustable Interest Rate (LIBOR) Act was signed into law. This law provides a statutory fallback mechanism on a nationwide basis to replace LIBOR with a benchmark rate that is selected by the Board of Governors of the Federal Reserve System and based on the Secured Overnight Financing Rate for certain contracts that reference LIBOR and contain no, or insufficient, fallback provisions. It is expected that implementing regulations in respect of the law will follow. The transition of investments from LIBOR to a replacement rate as a result of amendment, application of existing fallbacks, statutory requirements or otherwise may also result in a reduction in the value of certain instruments held by the Fund, a change in the cost of borrowing or the dividend rate for any preferred shares that may be issued by the Fund, or a reduction in the effectiveness of related Fund transactions such as hedges. Any such effects of the transition away from LIBOR, as well as other unforeseen effects, could result in losses to the Fund.

Regulatory Risk – Commodity Pool Operator

The CFTC has adopted regulations that subject registered investment companies and their investment advisers to regulation by the CFTC if the registered investment company invests more than a prescribed level of its liquidation value in futures, options on futures or commodities, swaps, or other financial instruments regulated under the CEA and the rules thereunder (“commodity interests”), or if the Fund markets itself as providing investment exposure to such instruments. The Investment Manager is registered with the CFTC as a CPO. However, with respect to the Fund, the Investment Manager has claimed an exclusion from registration as a CPO pursuant to CFTC Rule 4.5. For the Investment Manager to remain eligible for this exclusion, the Fund must comply with certain limitations, including limits on its ability to use any commodity interests and limits on the manner in which the Fund holds out its use of such commodity interests. These limitations may restrict the Fund’s ability to pursue its investment objective and strategies increase the costs of implementing its strategies, result in higher expenses for the Fund, and/or adversely affect the Fund’s total return. To the extent the Fund becomes ineligible for this exclusion from CFTC regulation, the Fund may consider steps in order to continue to qualify for exemption from CFTC regulation, or may determine to operate subject to CFTC regulation.

Liquidity Risk

Liquidity risk exists when particular investments are difficult to purchase or sell. Illiquid investments are investments that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. Illiquid investments may become harder to value, especially in changing markets. The Fund’s investments in illiquid investments may reduce the returns of the Fund because it may be unable to sell the illiquid investments at an advantageous time or price or possibly require the Fund to dispose of other investments at unfavorable times or prices in order to satisfy its

obligations, which could prevent the Fund from taking advantage of other investment opportunities. Additionally, the market for certain investments may become illiquid under adverse market or economic conditions independent of any specific adverse changes in the conditions of a particular issuer. Bond markets have consistently grown over the past three decades while the capacity for traditional dealer counterparties to engage in fixed income trading has not kept pace and in some cases has decreased. As a result, dealer inventories of corporate bonds, which provide a core indication of the ability of financial intermediaries to “make markets,” are at or near historic lows in relation to market size. Because market makers seek to provide stability to a market through their intermediary services, a significant reduction in dealer inventories could potentially lead to decreased liquidity and increased volatility in the fixed income markets. Such issues may be exacerbated during periods of economic uncertainty. In such cases, the Fund, due to the difficulty in purchasing and selling such securities or instruments, may be unable to achieve its desired level of exposure to a certain sector. To the extent that the Fund invests in securities of companies with smaller market capitalizations, foreign (non-U.S.) securities, Rule 144A securities, illiquid sectors of fixed income securities, derivatives or securities with substantial market and/or credit risk, the Fund will tend to have greater exposure to liquidity risk.

Tax Risk

The Fund has elected to be treated as a RIC under the Code and intends each year to qualify and be eligible to be treated as such, so that it generally will not be subject to U.S. federal income tax on its net investment income or net short-term or long-term capital gains that are distributed to shareholders. In order to qualify and be eligible for such treatment, the Fund must meet certain asset diversification tests, derive at least 90% of its gross income for such year from certain types of qualifying income, and distribute to its shareholders at least 90% of its “investment company taxable income” as that term is defined in the Code (which includes, among other things, dividends, taxable interest and the excess of any net short-term capital gains over net long-term capital losses, as reduced by certain deductible expenses).

[ ] | Base Prospectus 42

PIMCO Municipal Income Fund

affect the Fund’s ability to qualify or be eligible for treatment as a RIC. Income and gains from certain of the Fund’s activities may not constitute qualifying income to a RIC for purposes of the 90% gross income test. If the Fund were to treat income or gain from a particular investment or activity as qualifying income and the income or gain were later determined not to constitute qualifying income and, together with any other nonqualifying income, caused the Fund’s nonqualifying income to exceed 10% of its gross income in any taxable year, the Fund would fail to qualify as a RIC unless it is eligible to and does pay a tax at the Fund level.

If, in any year, the Fund were to fail to qualify for treatment as a RIC under the Code, and were ineligible to or did not otherwise cure such failure, the Fund would be subject to tax on its taxable income at corporate rates and, when such income is distributed, shareholders would be subject to further tax, on such distributions to the extent of the Fund’s current or accumulated earnings and profits.

Portfolio Turnover Risk

The Investment Manager manages the Fund without regard generally to restrictions on portfolio turnover. The use of futures contracts and other derivative instruments with relatively short maturities may tend to exaggerate the portfolio turnover rate for the Fund. Trading in fixed income securities does not generally involve the payment of brokerage commissions, but does involve indirect transaction costs. The use of futures contracts and other derivative instruments may involve the payment of commissions to futures commission merchants or other intermediaries. Higher portfolio turnover involves correspondingly greater expenses to the Fund, including brokerage commissions or dealer mark-ups and other transaction costs on the sale of securities and reinvestments in other securities. The higher the rate of portfolio turnover of the Fund, the higher these transaction costs borne by the Fund generally will be. Such sales may result in realization of taxable capital gains (including short-term capital gains, which are generally taxed to shareholders at ordinary income tax rates when distributed net of short-term capital losses and net long-term capital losses), and may adversely impact the Fund’s after-tax returns.

Operational Risk

Other Investment Companies Risk

with respect to assets so invested. Common Shareholders could therefore be subject to duplicative expenses to the extent the Fund invests in other investment companies. In addition, the securities of other investment companies may also be leveraged and will therefore be subject to the same leverage risks.

Cybersecurity Risk

Cyber security failures or breaches may result in financial losses to the Fund and its shareholders. These failures or breaches may also result in disruptions to business operations, potentially resulting in financial losses; interference with the Fund’s ability to calculate its NAV, process shareholder transactions or otherwise transact business with shareholders; impediments to trading; violations of applicable privacy and other laws; regulatory fines; penalties; third party claims in litigation; reputational damage; reimbursement or other compensation costs; additional compliance and cyber security risk management costs and other adverse consequences. In addition, substantial costs may be incurred in order to prevent any cyber incidents in the future.

43 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

to gain unauthorized access to systems from time to time, and there is no guarantee that efforts to prevent or mitigate the effects of such attacks or other attempts to gain unauthorized access will be successful. There is also a risk that cyber security breaches may not be detected. The Fund and its shareholders may suffer losses as a result of a cyber security breach related to the Fund, its service providers, trading counterparties or the issuers in which the Fund invests.

Potential Conflicts of Interest Risk—Allocation of Investment Opportunities

Repurchase Agreements Risk

Structured Investments Risk

Holders of structured products, including structured notes, credit-linked notes and other types of structured products, bear the risks of the underlying investments, index or reference obligation and are subject to counterparty risk. The Fund may have the right to receive payments only from the structured product, and generally does not have direct rights against the issuer or the entity that sold the assets to be securitized. While certain structured products enable the investor to acquire interests in a pool of securities without the brokerage and other expenses associated with directly holding the same securities, investors in structured products generally pay their share of the structured product’s administrative and other expenses. Although it is difficult to predict whether the prices of indices and securities underlying structured products will rise or fall, these prices (and, therefore, the prices of structured products) are generally influenced by the same types of political and economic events that affect issuers of securities and

capital markets generally. If the issuer of a structured product uses shorter term financing to purchase longer term securities, the issuer may be forced to sell its securities at below market prices if it experiences difficulty in obtaining such financing, which may adversely affect the value of the structured products owned by the Fund. Structured products generally entail risks associated with derivative instruments.

Market Disruptions Risk

Certain Affiliations

Certain broker-dealers may be considered to be affiliated persons of the Fund and/or the Investment Manager due to their possible affiliations with Allianz SE, the ultimate parent of the Investment Manager. Absent an exemption from the SEC or other regulatory relief, the Fund is generally precluded from effecting certain principal transactions with affiliated brokers, and its ability to purchase securities being underwritten by an affiliated broker or a syndicate including an affiliated broker, or to utilize affiliated brokers for agency transactions, is subject to restrictions. This could limit the Fund’s ability to engage in securities transactions and take advantage of market opportunities.

[ ] | Base Prospectus 44

PIMCO Municipal Income Fund

Anti-Takeover Provisions

The Declaration includes provisions that could limit the ability of other entities or persons to acquire control of the Fund or to convert the Fund to open-end status. See “Anti-Takeover and Other Provisions in the Declaration of Trust and Bylaws.” These provisions in the Declaration could have the effect of depriving the Common Shareholders of opportunities to sell their Common Shares at a premium over the then-current market price of the Common Shares or at NAV.

Distribution Rate Risk

AMT Bonds Risk

Focused Investment Risk

Substantial exposure to municipal bonds of particular issuers, geographies and/or jurisdictions will result in susceptibility to political, economic, regulatory and other factors affecting issuers of such bonds, their ability to meet their obligations and the economic condition of the facility or specific revenue source from whose revenues payments of obligations may be made. The ability of state, county, or local governments or other issuers to meet their obligations will depend primarily on the availability of tax and other revenues to those entities. The amounts of tax and other revenues available to issuers may be affected from time to time by economic, political and demographic

conditions that specifically impact such issuers. In addition, there are constitutional and statutory restrictions that limit the power of certain issuers to raise revenues or increase taxes. The availability of federal, state and local aid to issuers may also affect their ability to meet their obligations. The creditworthiness of obligations issued by local issuers within a given state may be unrelated to the creditworthiness of obligations issued by the state and there is no obligation on the part of the state to make payment on such local obligations in the event of default. Any reduction in the actual or perceived ability of an issuer to meet its obligations (including a reduction in the rating of its outstanding securities) would likely affect adversely the market value and marketability of its obligations and could adversely affect the values of other bonds as well. Moreover, in such circumstances, the value of the Fund’s shares may fluctuate more widely than the value of shares of a more diversified fund.

CSDR Related Risk

45 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

discipline regime, such expenses and penalties may be charged to the relevant Fund depending upon their characterization under the Fund’s Investment Management Agreement.

Insurance Risk

How the Fund Manages Risk

The Fund may (but is not required to) use various investment strategies to attempt to hedge exposure to reduce the risk of price fluctuations of its portfolio securities, the risk of loss, and to preserve capital. Derivatives strategies and instruments that the Fund may use include, among others, reverse repurchase agreements; interest rate swaps; total return swaps; credit default swaps; basis swaps; other types of swap agreements or options thereon; dollar rolls; futures and forward contracts (including foreign currency exchange contracts); short sales; options on financial futures; options based on either an index of municipal securities or taxable debt securities whose prices, PIMCO believes, correlate with the prices of the Fund’s investments; other derivative transactions; loans of portfolio securities and when-issued, delayed delivery and forward commitment transactions. Income earned by the Fund from its hedging and related transactions may be subject to one or more special U.S. federal income tax rules that can affect the

amount, timing and/or character of distributions to holders of the Fund’s Common Shares. For instance, many hedging activities will be treated as capital gain and, if not offset by net realized capital loss, will be distributed to shareholders in taxable distributions. If effectively used, hedging strategies will offset in varying percentages losses incurred on the Fund’s investments due to adverse interest rate changes. There is no assurance that these hedging strategies will be available at any time or that PIMCO will determine to use them for the Fund or, if used, that the strategies will be successful. PIMCO may determine not to engage in hedging strategies or to do so only in unusual circumstances or market conditions. In addition, the Fund may be subject to certain restrictions on its use of hedging strategies imposed by guidelines of one or more ratings agencies that may issue ratings on any Preferred Shares issued by the Fund.

The Fund may take certain actions if short-term interest rates increase or market conditions otherwise change (or the Fund anticipates such an increase or change) and the Fund’s leverage begins (or is expected) to adversely affect Common Shareholders. In order to attempt to offset such a negative impact of leverage on Common Shareholders, the Fund may shorten the average maturity or duration of its investment portfolio (by investing in short-term, high quality securities or implementing certain hedging strategies). The Fund also may attempt to reduce leverage by redeeming or otherwise purchasing any Preferred Shares (subject to any restrictions discussed under “Description of Capital Structure—Preferred Shares Redemption”), unwinding TOBs or by reducing any holdings in other instruments that create leverage. As explained above under “Principal Risks of the Fund—Leverage Risk,” the success of any such attempt to limit leverage risk depends on PIMCO’s ability to accurately predict interest rate or other market changes. Because of the difficulty of making such predictions, the Fund may not be successful in managing its interest rate exposure in the manner described above.

In addition, the Fund has adopted certain investment limitations designed to limit investment risk. See “Fundamental Investment Restrictions” in the Statement of Additional Information for a description of these limitations.

[ ] | Base Prospectus 46

PIMCO Municipal Income Fund

Management of the Fund

Trustees and Officers

The business of the Fund is managed under the direction of the Fund’s Board, including supervision of the duties performed by the Investment Manager. The Board is currently composed of nine Trustees of the Fund (“Trustees”), two of whom are treated as “interested persons” of the Fund (as defined in the 1940 Act). The names and business addresses of the Trustees and officers of the Fund and their principal occupations and other affiliations during the past five years are set forth under “Management of the Fund” in the Statement of Additional Information.

Investment Manager

PIMCO serves as the investment manager of the Fund. Subject to the supervision of the Board. PIMCO is responsible for managing the investment activities of the Fund and the Fund’s business affairs and other administrative matters.

PIMCO is located at 650 Newport Center Drive, Newport Beach, CA, 92660. Organized in 1971, PIMCO provides investment management and advisory services to private accounts of institutional and individual clients and to registered investment companies. PIMCO is a majority-owned indirect subsidiary of Allianz SE, a publicly traded European insurance and financial services company. As of June 30, 2022, PIMCO had approximately $1.82 trillion of assets under management. As of June 30, 2022, PIMCO had $1.43 trillion of third-party assets under management.

David Hammer is primarily responsible for the day-to-day portfolio management of the Fund.

Portfolio Manager	Since	Recent Professional Experience
David Hammer	2015	Mr. Hammer is a Managing Director and municipal bond portfolio manager in the Newport Beach office. He rejoined PIMCO in 2015 from Morgan Stanley, where he was managing director and head of municipal trading, risk management and research. Previously at PIMCO, he was a senior vice president and municipal bond portfolio manager, and prior to joining PIMCO in 2012, he was an executive director and head of the high yield and distressed municipal bond trading group at Morgan Stanley.

Control Persons

A control person is a person who owns, either directly or indirectly, beneficially more than 25% of the voting securities of a company. As of [ ], the Fund did not know of any person or entity who “controlled” the Fund.

Additional Information

The Trustees are responsible generally for overseeing the management of the Fund. The Trustees authorize the Fund to enter into service agreements with the Investment Manager and other service providers in order to provide, and in some cases authorize service providers to procure through other parties, necessary or desirable services on behalf of the Fund. Shareholders are not intended to be third-party beneficiaries of such service agreements.

Neither this prospectus, the Fund’s Statement of Additional Information, any contracts filed as exhibits to the Fund’s registration statement, nor any other communications or disclosure documents from or on behalf of the Fund creates a contract between a shareholder of the Fund and the Fund, a service provider to the Fund, and/or the Trustees or officers of the Fund. The Trustees may amend this prospectus, the Statement of Additional Information, and any other contracts to which the Fund is a party, and interpret the investment objective, policies, restrictions and contractual provisions applicable to the Fund without shareholder input or approval, except in circumstances in which shareholder approval is specifically required by law (such changes to fundamental investment policies) or where a shareholder approval requirement is specifically disclosed in the Fund's prospectus or Statement of Additional Information.

Investment Management Agreement

Pursuant to an investment management agreement between the Investment Manager and the Fund (the “Investment Management Agreement”), the Fund has agreed to pay the Investment Manager an annual fee, payable monthly, in an amount equal to 0.705 of the Fund’s average daily net asset value (including daily net assets attributable to any Preferred Shares) for the services rendered, for the facilities it provides and for certain expenses borne by the Investment Manager pursuant to the Investment Management Agreement. Average daily net asset value includes total assets of the Fund (including daily net assets attributable to any Preferred Shares) minus accrued liabilities.

Pursuant to the Investment Management Agreement, PIMCO shall provide to the Fund investment guidance and policy direction in connection with the management of the Fund, including oral and written research, analysis, advice and statistical and economic data and information. In addition, under the terms of the Investment Management Agreement, subject to the general supervision of the Board, the Investment Manager shall provide or cause to be furnished all supervisory and administrative and other services reasonably necessary for the operation of the Fund under the unified management fee structure, including but not limited to the supervision and coordination of matters relating to the operation of the Fund, including any necessary coordination among the custodian, transfer agent, dividend disbursing agent and recordkeeping agent (including pricing and valuation

47 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

of the Fund), accountants, attorneys, auction agents and other parties performing services or operational functions for the Fund; the provision of adequate personnel, office space, communications facilities, and other facilities necessary for the effective supervision and administration of the Fund, as well as the services of a sufficient number of persons competent to perform such supervisory and administrative and clerical functions as are necessary for compliance with federal securities laws and other applicable laws; the maintenance of the books and records of the Fund; the preparation of all federal, state, local and foreign tax returns and reports for the Fund; provision of administrative services to shareholders for the Fund including the maintenance of a shareholder information telephone number; the provision of certain statistical information and performance of the Fund, an internet website (if requested), and maintenance of privacy protection systems and procedures; the preparation and filing of such registration statements and other documents with such authorities as may be required to register and maintain the listing of the shares of the Fund; the taking of other such actions as may be required by applicable law (including establishment and maintenance of a compliance program for the Fund); and the preparation, filing and distribution of proxy materials, periodic reports to shareholders and other regulatory filings.

In addition, under the Investment Management Agreement, the Investment Manager will procure, at its own expense, the following services, and will bear expenses associated with the following for the Fund: a custodian or custodians for the Fund to provide for the safekeeping of the Fund’s assets; a recordkeeping agent to maintain the portfolio accounting records for the Fund; a transfer agent for the Fund; a dividend disbursing agent and/or registrar for the Fund; all audits by the Fund’s independent public accountant (except fees to auditors associated with satisfying rating agency requirements for preferred shares or other securities issued by the Fund and other related requirements in the Fund’s organizational documents); valuation services; maintaining the Fund’s tax records; all costs and/or fees incident to meetings of the Fund’s shareholders, the preparation, printing and mailing of the Fund’s prospectuses (although the Fund will bear such expenses in connection with the offerings made pursuant to this prospectus as noted below) notices and proxy statements, press releases and reports to its Shareholders, the filing of reports with regulatory bodies, the maintenance of the Fund’s existence and qualification to do business, the expense of issuing, redeeming, registering and qualifying for sale, Common Shares with the federal and state securities authorities, and the expense of qualifying and listing Shares with any securities exchange or other trading system; legal services (except for extraordinary legal expenses); costs of printing certificates representing Shares of the Fund; the Fund’s pro rata portion of its fidelity bond and other insurance premiums; and association membership dues.

The Fund (and not Investment Manager) will be responsible for certain fees and expenses that are not covered by the unified fee under the Investment Management Agreement. These include fees and expenses, including travel expenses, and fees and expenses of legal counsel retained for their benefit, of Trustees who are not officers, employees, partners, shareholders or members of PIMCO or its subsidiaries or affiliates; the salaries and other compensation or expenses, including travel expenses, of any of the Fund’s executive officers and employees, if any, who are not officers, directors, shareholders, members, partners or employees of Investment Manager or its subsidiaries or affiliates; taxes and governmental fees, if any, levied against the Fund; brokerage fees and commissions and other portfolio transaction expenses incurred by or for the Fund (including, without limitation, fees and expenses of outside legal counsel or third-party consultants retained in connection with reviewing, negotiating, and structuring specialized loans and other investments made by the Fund and subject to specific or general authorization by the Fund’s Board of Trustees (for example so-called “broken-deal costs” (e.g., fees, costs, expenses and liabilities, including, for example, due diligence-related fees, costs, expenses and liabilities, with respect to unconsummated investments))); expenses of the Fund’s securities lending (if any), including any securities lending agent fees, as governed by a separate securities lending agreement; costs, including interest expenses, of borrowing money or engaging in other types of leverage financing including, without limitation, through the use by the Fund of reverse repurchase agreements, TOBs, bank borrowings and credit facilities; costs, including dividend and/or interest expenses and other costs (including, without limitation, offering and related legal costs, fees to brokers, fees to auction agents, fees to transfer agents, fees to ratings agencies and fees to auditors associated with satisfying ratings agency requirements for Preferred Shares or other securities issued by the Fund and other related requirements in the Fund’s organizational documents) associated with the Fund’s issuance, offering, redemption and maintenance of Preferred Shares, commercial paper or other senior securities for the purpose of incurring leverage; fees and expenses of any underlying funds or other pooled vehicles in which the Fund invests; dividend and interest expenses on short positions taken by the Fund; organizational and offering expenses of the Fund, including with respect to share offerings following the Fund’s initial offering, such as rights and shelf offerings (including expenses associated with offerings made pursuant to this prospectus), and expenses associated with tender offers and other share repurchases and redemptions; extraordinary expenses, including extraordinary legal expenses as may arise, including expenses incurred in connection with litigation, proceedings, other claims, and the legal obligations of the Fund to indemnify its Trustees, officers, employees, shareholders, distributors, and agents with respect thereto; and expenses of the Fund which are capitalized in accordance with generally accepted accounting principles.

A discussion regarding the considerations of the Fund’s Board for approving the Investment Management Agreement between PIMCO and the Fund is available in the Fund’s semi-annual report to shareholders for the period ended June 30, 2022.

[ ] | Base Prospectus 48

PIMCO Municipal Income Fund

Net Asset Value

The NAV of the Fund’s Common Shares is determined by dividing the total value of the Fund’s portfolio investments and other assets, less any liabilities, by the total number of common shares outstanding.

On each day that the NYSE is open, Fund shares are ordinarily valued as of the close of regular trading (normally 4:00 p.m., Eastern time) (“NYSE Close”). Information that becomes known to the Fund or its agents after the time as of which NAV has been calculated on a particular day will not generally be used to retroactively adjust the price of a security or the NAV determined earlier that day. If regular trading on the NYSE closes earlier than scheduled, the Fund may calculate its NAV as of the earlier closing time or calculate its NAV as of the normally scheduled close of regular trading on the NYSE for that day. The Fund generally does not calculate its NAV on days on which the NYSE is not open for business. If the NYSE is closed on a day it would normally be open for business, the Fund may calculate its NAV as of the normally scheduled NYSE Close or such other time that the Fund may determine. The Fund reserves the right to change the time as of which its NAV is calculated if the Fund closes earlier, or as permitted by the SEC.

For purposes of calculating NAV, portfolio securities and other assets for which market quotes are readily available are valued at market value. Market value is generally determined on the basis of official closing prices or the last reported sales prices, or if no sales are reported, based on quotes obtained from established market makers or prices (including evaluated prices) supplied by the Fund’s approved pricing services, quotation reporting systems and other third-party sources (together, “Pricing Services”). The Fund will normally use pricing data for domestic equity securities received shortly after the NYSE Close and does not normally take into account trading, clearances or settlements that take place after the NYSE Close. A foreign (non-U.S.) equity security traded on a foreign exchange or on more than one exchange is typically valued using pricing information from the exchange considered by PIMCO to be the primary exchange. A foreign (non-U.S.) equity security will be valued as of the close of trading on the foreign exchange, or the NYSE Close, if the NYSE Close occurs before the end of trading on the foreign exchange. Domestic and foreign (non-U.S.) fixed income securities, non-exchange traded derivatives, and equity options are normally valued on the basis of quotes obtained from brokers and dealers or Pricing Services using data reflecting the earlier closing of the principal markets for those securities. Prices obtained from Pricing Services may be based on, among other things, information provided by market makers or estimates of market values obtained from yield data relating to investments or securities with similar characteristics. Certain fixed income securities purchased on a delayed-delivery basis are marked to market daily until settlement at the forward settlement date. Exchange-traded options, except equity options, futures and options on futures are valued at the settlement price determined by the relevant exchange. Swap agreements are valued on the basis of bid quotes obtained from brokers and dealers or market-based prices supplied by Pricing Services or other pricing sources. With respect to any portion of the Fund’s assets that are invested in one or more open-end management investment companies (including those advised by PIMCO) (other than ETFs), the Fund’s NAV will be calculated based upon the NAVs of such investments.

Investments for which market quotes or market-based valuations are not readily available are valued at fair value as determined in good faith by the Board or persons acting at their direction. The Board has adopted methods for valuing securities and other assets in circumstances where market quotes are not readily available, and has delegated to PIMCO the responsibility for applying the fair valuation methods. In the event that market quotes or market-based valuations are not readily available, and the security or asset cannot be valued pursuant to a Board approved valuation method, the value of the security or asset will be determined in good faith by the Valuation Oversight Committee of the Board (“Valuation Oversight Committee”), generally based on recommendations provided by PIMCO. Market quotes are considered not readily available in circumstances where there is an absence of current or reliable market-based data (e.g., trade information, bid/ask information, indicative market quotations (“Broker Quotes”), Pricing Services’ prices), including where events occur after the close of the relevant market, but prior to the NYSE Close, that materially affect the values of the Fund’s securities or assets. In addition, market quotes are considered not readily available when, due to extraordinary circumstances, the exchanges or markets on which the securities trade do not open for trading for the entire day and no other market prices are available. The Board has delegated to PIMCO the responsibility for monitoring significant events that may materially affect the values of the Fund’s securities or assets and for determining whether the value of the applicable securities or assets should be reevaluated in light of such significant events.

When the Fund uses fair valuation to determine the value of a portfolio security or other asset for purposes of calculating its NAV, such investments will not be priced on the basis of quotes from the primary market in which they are traded, but rather may be priced by another method that the Board or persons acting at their direction believe reflects fair value. Fair valuation may require subjective determinations about the value of a security. While the Fund’s policy is intended to result in a calculation of the Fund’s NAV that fairly reflects security values as of the time of pricing, the Fund cannot ensure that fair values determined by the Board or persons acting at their direction would accurately reflect the price that the Fund could obtain for a security if it were to dispose of that security as of the time of pricing (for instance, in a forced or distressed sale). The prices used by the Fund may differ from the value that would be realized if the securities were sold.

On December 3, 2020, the SEC adopted Rule 2a-5 under the 1940 Act, which is intended to address valuation practices and the role of the board of directors with respect to the fair value of the investments of a registered investment company or business development company. Among other things, Rule 2a-5 will permit the fund’s board to designate the fund’s primary investment adviser to perform the fund’s fair value determinations,

49 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

which will be subject to board oversight and certain reporting and other requirements intended to ensure that the board receives the information it needs to oversee the investment adviser’s fair value determinations. Compliance with Rule 2a-5 will not be required until September 8, 2022. PIMCO continues to review Rule 2a-5 and its impact on PIMCO’s and the Fund’s valuation policies and related practices.

Distributions

The Fund makes regular monthly cash distributions to Common Shareholders at a rate based upon the past and projected net income of the Fund. Subject to applicable law, the Fund may fund a portion of its distributions with gains from the sale of portfolio securities and other sources. Distributions can only be made from net investment income after paying any accrued dividends to holders of the Preferred Shares. The dividend rate that the Fund pays on its Common Shares may vary as portfolio and market conditions change, and will depend on a number of factors, including without limit the amount of the Fund’s undistributed net investment income and net short- and long-term capital gains, as well as the costs of any leverage obtained by the Fund (including the amount of the costs and dividend rates on the outstanding Preferred Shares and interest or other expenses on any TOBs, reverse repurchase agreements, credit default swaps, dollar rolls/buy backs and borrowings). As portfolio and market conditions change, the rate of distributions on the Common Shares and the Fund’s dividend policy could change. There can be no assurance that a change in market conditions or other factors will not result in a change in the Fund distribution rate or that the rate will be sustainable in the future. See “Principal Risks of the Fund—Fund Distribution Rates.” For a discussion of factors that may cause the Fund’s income and capital gains (and therefore the dividend) to vary, see “Principal Risks of the Fund.” The Fund generally distributes each year all of its net investment income and net short-term capital gains. In addition, at least annually, the Fund generally distributes net realized long-term capital gains not previously distributed, if any. The net investment income of the Fund consists of all income (other than net short-term and long-term capital gains) less all expenses of the Fund (after it pays accrued dividends on the outstanding Preferred Shares).

To permit the Fund to maintain a more level monthly distribution, the Fund may distribute less than the entire amount of net investment income earned in a particular period. The undistributed net investment income would be available to supplement future distributions. As a result, the distributions paid by the Fund for any particular monthly period may be more or less than the amount of net investment income actually earned by the Fund during the period. Undistributed net investment income will be additive to the Fund’s NAV and, correspondingly, distributions from undistributed net investment income will be deducted from the Fund’s NAV.

The tax treatment and characterization of the Fund’s distributions may vary significantly from time to time because of the varied nature of the Fund’s investments. For example, the Fund may enter into opposite sides of multiple interest rate swaps or other derivatives with respect to the same underlying reference instrument (e.g., a 10-year U.S. treasury) that have different effective dates with respect to interest accrual time periods for the principal purpose of generating distributable gains (characterized as ordinary income for tax purposes) that are not part of the Fund’s duration or yield curve management strategies. In such a “paired swap transaction”, the Fund would generally enter into one or more interest rate swap agreements whereby the Fund agrees to make regular payments starting at the time the Fund enters into the agreements equal to a floating interest rate in return for payments equal to a fixed interest rate (the “initial leg”). The Fund would also enter into one or more interest rate swap agreements on the same underlying instrument, but take the opposite position (i.e., in this example, the Fund would make regular payments equal to a fixed interest rate in return for receiving payments equal to a floating interest rate) with respect to a contract whereby the payment obligations do not commence until a date following the commencement of the initial leg (the “forward leg”). The Fund may engage in investment strategies, including those that employ the use of derivatives, to, among other things, seek to generate current, distributable income, even if such strategies could potentially result in declines in the Fund’s net asset value (“NAV”). The Fund’s income and gain-generating strategies, including certain derivatives strategies, may generate current income and gains taxable as ordinary income sufficient to support monthly distributions even in situations when the Fund has experienced a decline in net assets due to, for example, adverse changes in the broad U.S. or non-U.S. equity markets or the Fund’s debt investments, or arising from its use of derivatives. Because some or all of these transactions may generate capital losses without corresponding offsetting capital gains, portions of the Fund’s distributions recognized as ordinary income for tax purposes (such as from paired swap transactions) may be economically similar to a taxable return of capital when considered together with such capital losses. The tax treatment of certain derivatives in which the Fund invests may be unclear and thus subject to recharacterization. Any recharacterization of payments made or received by the Fund pursuant to derivatives potentially could affect the amount, timing or character of Fund distributions. In addition, the tax treatment of such investment strategies may be changed by regulation or otherwise.

To the extent required by the 1940 Act and other applicable laws, absent an exemption, a notice will accompany each monthly distribution with respect to the estimated source (as between net income, gains or other capital source) of the distribution made. If the Fund estimates that a portion of one of its dividend distributions may be comprised of amounts from sources other than net income in accordance with its policies and good accounting practices, the Fund will notify shareholders of record of the estimated composition of such distribution through a Section 19 Notice. For these purposes, the Fund estimates the source or sources from which a distribution is paid, to the close of the period as of which it is paid, in reference to its internal accounting records and related accounting practices. If, based on such accounting records and practices, it is estimated that a particular distribution does not include capital gains or paid-in surplus or other capital sources, a Section 19 Notice generally would not be issued. It is important to note that differences exist between the Fund’s daily internal accounting records and practices, the Fund’s financial statements

[ ] | Base Prospectus 50

PIMCO Municipal Income Fund

presented in accordance with U.S. GAAP, and recordkeeping practices under income tax regulations. For instance, the Fund’s internal accounting records and practices may take into account, among other factors, tax-related characteristics of certain sources of distributions that differ from treatment under U.S. GAAP. Examples of such differences may include, among others, the treatment of paydowns on mortgage-backed securities purchased at a discount and periodic payments under interest rate swap contracts. Accordingly, among other consequences, it is possible that the Fund may not issue a Section 19 Notice in situations where the Fund’s financial statements prepared later and in accordance with U.S. GAAP and/or the final tax character of those distributions might later report that the sources of those distributions included capital gains and/or a return of capital.

The tax characterization of the Fund’s distributions made in a taxable year cannot finally be determined until at or after the end of such taxable year. As a result, there is a possibility that the Fund may make total distributions during a taxable year in an amount that exceeds the Fund’s net investment income and net realized capital gains (as reduced by any capital loss carry-forwards) for the relevant year. For example, the Fund may distribute amounts early in the year that are derived from short-term capital gains, but incur net short-term capital losses later in the year, thereby offsetting short-term capital gains out of which the Fund has already made distributions. In such a situation, the amount by which the Fund’s total distributions exceed net investment income and net realized capital gains would generally be treated as a tax-free return of capital up to the amount of a shareholder’s tax basis in his or her Common Shares, with any amounts exceeding such basis treated as gain from the sale of Common Shares. In general terms, a return of capital would occur where the Fund distribution (or portion thereof) represents a return of a portion of your investment, rather than net income or capital gains generated from your investment during a particular period. A return of capital distribution is not taxable, but it reduces a shareholder’s tax basis in the Common Shares, thus reducing any loss or increasing any gain on a subsequent taxable disposition by the shareholder of the Common Shares. The Fund will prepare and make available to shareholders detailed tax information with respect to the Fund’s distributions annually. See “Tax Matters.”

Dividend Reinvestment Plan

The information contained under the heading “Dividend Reinvestment Plan” in the Fund’s Annual Report is incorporated herein by reference.

Description of Capital Structure

The following is a brief description of the capital structure of the Fund. This description does not purport to be complete and is subject to and qualified in its entirety by reference to the Declaration and the Fund’s Bylaws, as amended and restated through the date hereof (the “Bylaws”). The Declaration and Bylaws are each exhibits to the registration statement of which this prospectus is a part.

The Fund is an unincorporated voluntary association with transferable shares of beneficial interest (commonly referred to as a “Massachusetts business trust”) established under the laws of the Commonwealth of Massachusetts by the Declaration. The Declaration provides that the Trustees of the Fund may authorize separate classes of shares of beneficial interest. Preferred shares (such as the ARPS and the RVMTP Shares) are permitted to be issued in one or more series, with such par value and with such rights as determined by the Board, by action of the Board without the approval of the Common Shareholders.

The following table shows, for each class of authorized securities of the Fund, the amount of (i) shares authorized and (ii) shares outstanding, each as of July 31, 2022.

Title of Class	Amount Authorized	Amount Outstanding
Common Shares	Unlimited	26,091,140
Preferred Shares
Series A ARPS	1,600	1,310
Series B ARPS	1,600	1,367
Series C ARPS	1,600	1,294
Series D ARPS	1,600	1,388
Series E ARPS	1,600	1,309
Series 2051 RVMTP Shares	Unlimited	233

51 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

The Common Shares of the Fund commenced trading on the NYSE in June 2001, under the trading or “ticker” symbol “PMF.” As of the close of trading on the NYSE on [ ], the NAV per Common Share was $[ ], and the closing price per Common Share on the NYSE was $[ ], representing a premium to NAV of [ ]%.

Common Shareholders will be entitled to the payment of dividends and other distributions when, as and if declared by the Board after payment of preferential amounts payable to holders of Preferred Shares. All Common Shares have equal rights to the payment of dividends and the distribution of assets upon liquidation after payment of the preferential amounts payable to holders of Preferred Shares. Common Shares will, when issued, be fully paid and, subject to matters discussed in “Anti-Takeover and Other Provisions in the Declaration of Trust,” non-assessable, and will have no pre-emptive or conversion rights or rights to cumulative voting. Upon liquidation of the Fund, after paying or adequately providing for the payment of all liabilities of the Fund and the liquidation preference with respect to any outstanding Preferred Shares, and upon receipt of such releases, indemnities and refunding agreements as they deem necessary for their protection, the Trustees may distribute the remaining assets of the Fund among the Fund’s Common Shareholders.

Preferred Shares

The Declaration authorizes the issuance of an unlimited number of preferred shares. Preferred shares may be issued in one or more classes or series, with such par value and rights as determined by the Board of Trustees, by action of the Board of Trustees without the approval of the Common Shareholders.

The Fund initially issued ARPS in five series (Series A, Series B, Series C, Series D and Series E) in August 2001, in the amount of 1,600 shares per series. The ARPS have a par value of $0.00001 and liquidation value of $25,000 per share. The ARPS have various rights determined by action of the Board without the approval of Common Shareholders, most of which are specified in Article 11 of the Bylaws.

On September 18, 2018, the Fund issued 233 variable municipal term preferred shares in a single series (the “VMTP Shares”). On June 30, 2021, pursuant to the authority expressly vested in the Board, the Board authorized the redesignation of the Fund’s VMTP Shares as Remarketable Variable Rate MuniFund Term Preferred Shares, Series 2051 (the “RVMTP Shares” and, together with the ARPS and any other preferred shares the Fund may have outstanding, the “Preferred Shares”), effective July 14, 2021.

For so long as any Preferred Shares are outstanding, the Fund generally may not declare, pay or set apart for payment any dividend or other distribution (other than a dividend or distribution paid in shares of additional Common Shares or options, warrants or rights to subscribe for or purchase Common Shares or other shares ranking junior to the Preferred Shares as to dividends or upon liquidation) in respect of Common Shares or any other shares of the Fund ranking junior to or on a parity with the Preferred Shares as to dividends or upon liquidation, or call for redemption, redeem, purchase or otherwise acquire for consideration any Common Shares or any other such junior shares (except by conversion into or exchange for shares of beneficial interest of the Fund ranking junior to Preferred Shares as to dividends and upon liquidation) or any such parity shares (except by conversion into or exchange for shares of beneficial interest of the Fund ranking junior to or on a parity with Preferred Shares as to dividends and upon liquidation), unless and only if: (i) immediately after such transaction, the Fund would satisfy Moody’s Ratings Agency Preferred Shares Asset Coverage and 1940 Act Preferred Shares Asset Coverage (each as defined and described under “—Rating Agency Guidelines and Asset Coverage”); (ii) full cumulative dividends on the Preferred Shares due on or prior to the date of the transaction have been declared and paid or shall have been declared and sufficient funds for the payment thereof deposited with the auction agent for the Preferred Shares; and (iii) the Fund has redeemed the full number of Preferred Shares required to be redeemed by any provision for mandatory redemption contained in the Bylaws. See “Preferred Shares Redemption.” Further, so long as any Preferred Shares are outstanding, the Fund generally may not declare, pay or set apart for payment any dividend or other distribution on any parity shares other than the Preferred Shares unless the Fund contemporaneously declares, pays or sets apart for payment, as the case may be, the same proportionate share of dividends on the Preferred Shares. The Fund expects that similar restrictions would apply to any other classes of Preferred Shares that the Fund might choose to issue in the future. In addition, if the Fund has outstanding any senior security representing indebtedness, the 1940 Act prohibits the Fund from declaring any dividend or distribution on the Fund’s Common Shares (other than a dividend or distribution paid in shares of additional Common Shares) unless such senior securities representing indebtedness have, at the time of the declaration, asset coverage of at least 300% after deducting the amount of such dividend or distribution. See “Use of Leverage.”

Shareholders of each class are entitled to one vote for each share held. Common Shareholders will vote with the holders of any outstanding Preferred Shares as a single class on each matter submitted to a vote of holders of Common Shares, except as otherwise provided by the Declaration, the Bylaws or applicable law. Except as otherwise provided by the Declaration, the Bylaws or applicable law, holders of Preferred Shares, voting as a separate class, are entitled to elect two of the Fund’s Trustees. The remaining Trustees are elected by Common Shareholders and holders of Preferred Shares, voting together as a single class. In the unlikely event that two full years of accrued dividends are unpaid on the Preferred Shares, the holders of all outstanding Preferred Shares, voting as a separate class, will be entitled to elect a majority of the Fund’s Trustees until all dividends in arrears have been paid or declared and set apart for payment. The holders of Preferred Shares also have the right to elect a majority of the Fund’s Trustees as may be required under the 1940 Act.

[ ] | Base Prospectus 52

PIMCO Municipal Income Fund

The Preferred Shares have various rights that were approved by the Board without the approval of Common Shareholders, which are specified in the Fund’s Bylaws. Certain rights, terms and conditions the Preferred Shares are summarized below:

Distribution Preference. Any Preferred Shares, including, without limitation, the ARPS and the RVMTP Shares, have complete priority over the Common Shares as to distribution of assets.

Voting Rights. Under the 1940 Act, Preferred Shares (including, without limitation, the ARPS and the RVMTP Shares) are required to be voting shares and to have equal voting rights with Common Shares. Except as otherwise indicated in the Prospectus or this Statement of Additional Information, and except as otherwise required by applicable law, Preferred Shares vote together with Common Shareholders as a single class.

In addition, holders of Preferred Shares, including the ARPS and the RVMTP Shares, voting as a separate class, are entitled to elect two of the Fund’s trustees. The remaining trustees are elected by Common Shareholders and Preferred Shareholders, voting together as a single class. In the unlikely event that two full years of accrued dividends are unpaid on the Preferred Shares, the holders of all outstanding Preferred Shares voting as a separate class, are entitled to elect a majority of the Fund’s trustees until all dividends in arrears with respect to the Preferred Shares have been paid or declared and set apart for payment. In order for the Fund to take certain actions or enter into certain transactions, a separate class vote of Preferred Shareholders is required, in addition to the single class vote of the holders of Preferred Shares and Common Shares.

Liquidation Preference. Subject to the rights of holders of any series or class or classes of shares ranking on a parity with the Preferred Shares with respect to the distribution of assets upon liquidation of the Fund, upon a liquidation of the Fund (whether voluntary or involuntary), the holders of Preferred Shares then outstanding would be entitled to receive and to be paid, out of the assets of the Fund available for distribution to its shareholders, before any payment or distribution would be made on the Fund’s Common Shares or any other class of shares of the Fund ranking junior in right of payment upon liquidation to the Preferred Shares, an amount equal to the liquidation preference with respect to such Preferred Shares ($25,000 per share for the ARPS and $100,000 per share for the RVMTP Shares), plus an amount equal to all dividends thereon (whether or not earned or declared by the Fund, but excluding the interest thereon) accumulated but unpaid to (but not including) the date of final distribution in same-day funds in connection with the liquidation of the Fund. If such assets of the Fund are insufficient to make the full liquidation payment on outstanding Preferred Shares, then such assets will be distributed among the holders of Preferred Shares and the holders of shares of such other class or series ratably in proportion to the respective preferential amounts to which they are entitled. After the payment to the holders of Preferred Shares of the full preferential amounts provided for as described herein, the holders of Preferred Shares as such would have no right or claim to any of the remaining assets of the Fund. For these purposes, a liquidation of the Fund does not include the sale of all or any portion of the assets of the Fund or the merger, consolidation or statutory share exchange of the Fund into or with any trust or other entity.

As used in this prospectus, unless otherwise noted, the Fund’s “net assets” include assets of the Fund attributable to any outstanding Preferred Shares, with no deduction for the liquidation preference of the Preferred Shares. Solely for financial reporting purposes, however, the Fund is required to exclude the liquidation preference of the Preferred Shares from “net assets,” so long as the Preferred Shares have redemption features that are not solely within the control of the Fund. For all regulatory and tax purposes, the Fund’s Preferred Shares will be treated as stock (rather than indebtedness).

1940 Act Asset Coverage. In accordance with the Fund’s governing documents and the 1940 Act, the Fund is required to maintain certain asset coverage with respect to all outstanding senior securities of the Fund which are stocks for purposes of the 1940 Act, including the ARPS and the RVMTP Shares.

Under the 1940 Act, the Fund is not permitted to issue preferred shares unless, immediately after such issuance, the Fund has “asset coverage,” as defined in Section 18(h) of the 1940 Act (“1940 Act Asset Coverage”) with respect to at least 200% of the liquidation value of any outstanding preferred shares and the newly issued preferred shares plus the aggregate amount of any senior securities of the Fund representing indebtedness (i.e., such liquidation value plus the aggregate amount of senior securities representing indebtedness may not exceed 50% of the Fund’s total net assets). In addition, the Fund is not permitted to declare or pay common share dividends unless immediately thereafter the Fund has a minimum asset coverage ratio of 200% with respect to all outstanding senior securities of the Fund which are stocks for purposes of the 1940 Act after deducting the amount of such common share dividends.

Issuance of Additional Preferred Shares. So long as any Preferred Shares are outstanding, the Fund may, without the vote or consent of the holders thereof, authorize, establish and create and issue and sell shares of one or more series of Preferred Shares ranking on a parity with the ARPS and the RVMTP Shares as to the payment of dividends and the distribution of assets upon dissolution, liquidation or the winding up of the affairs of the Fund, in addition to then outstanding series of Preferred Shares, including additional series of RVMTP Shares, and authorize, issue and sell additional shares of any such Series of Preferred Shares then outstanding or so established or created, including additional series of RVMTP Shares, in each case in accordance with applicable law, provided that the Fund shall, immediately after giving effect to the issuance of such Preferred Shares and to its receipt and application of the proceeds thereof, including to the redemption of Preferred Shares with such proceeds, have “asset coverage,” as defined for the purposes of Section 18(h) of the Act, of at least 200%.

53 Base Prospectus | PIMCO Municipal Income Fund

Base Prospectus

Redemption. Although the Preferred Shares are subject to redemption under certain circumstances as described below, unlike the shares of an open-end mutual fund, the Preferred Shares may not be redeemed at a shareholder’s option at NAV or otherwise.

RVMTP SHARES

Dividends. The dividend rate paid on the RVMTP Shares is determined over the course of “Rate Period,” which generally begins each Thursday and ends the following Wednesday. The dividends per share for the RVMTP Shares for a given Rate Period are dependent on the RVMTP Share dividend rate (the “RVMTP Share Dividend Rate”) for that Rate Period. The RVMTP Share Dividend Rate for the RMVTP Shares is equal to the greater of (i) the sum of the “Index Rate”1 plus an “Applicable Spread”2 for the Rate Period plus the “Failed Remarketing Spread,”3 if applicable, and (ii) the sum of (a) the product of the Index Rate multiplied by the “Applicable Multiplier”4 for such Rate Period plus (b) 0.92% plus (c) the Failed Remarketing Spread, if applicable. The dividend per RVMTP Share for the Rate Period is then determined as described in the table below.5

Dividend Rate		Rate Period Fraction		RVMTP Shares Liquidation Preference		Dividend
Dividend Rate	X	Number of days in the Rate Period (or a part thereof) Divided by Total number of days in the year	X	100,000	=	Dividends per RVMTP Share

RVMTP Special Terms Period. The Fund, at its option, may designate special terms applicable to all of the outstanding RVMTP Shares for a certain period (a “Special Terms Period”) pursuant to a notice of special terms. Such special terms may differ from those provided in the current governing documents of the RVMTP Shares and may include, without limitation, changes to the RVMTP Dividend Rate, dividend payment dates, redemption provisions (including, without limitation, the RVMTP Term Redemption Date or the RVMTP Early Term Redemption Date), required Effective Leverage Ratio, and the Preferred Shareholder Gross-Up (each as defined below); provided that such special terms do not affect the parity ranking of the RVMTP Shares to any other class or series of Preferred Shares then outstanding with respect to dividends or distribution of assets upon dissolution, liquidation, or winding up of the affairs of the Fund. No Special Terms Period with respect to the RVMTP Shares will become effective unless certain conditions are satisfied, including that all of the RVMTP Shares are remarketed (except with respect to any RVMTP Shares whose holders have elected to retain their RVMTP Shares for the Special Terms Period). A Special Terms Period will not become effective before the 12-month anniversary of the date of original issue of the RVMTP Shares.

Preferred Shareholder Gross-Up. As noted above, RVMTP Shares each pay dividend distributions at stated rates, which rates are based generally on the assumption that such dividend distributions consist entirely of “exempt-interest dividends” (as defined below under “Taxation—Exempt-Interest Dividends”). The terms of the RVMTP Shares provide further that, in the event less than the entire amount of any particular dividend distribution paid pursuant to the stated rate were to consist of “exempt-interest dividends” (i.e., if a portion of any particular dividend were to derive from ordinary income or capital gain, including short-term capital gain taxable as ordinary income when distributed), the amount of such dividend would increase by an amount (the “Preferred Shareholder Gross-Up”) such that the after-tax amount of such dividend, as increased by the Preferred Shareholder Gross-Up, would equal the total amount the holder of such RVMTP Shares would have received if the dividend at the stated rate had consisted entirely of “exempt-interest dividends.” The Preferred Shareholder Gross-Up is calculated (i) without consideration being given to the time value of money, (ii) assuming that no holder of RVMTP Shares is subject to the federal alternative minimum tax, and (iii) assuming that the portion of any dividend distribution (including the amount of the Preferred Shareholder Gross-Up) that is not an exempt interest dividend would be taxable (x), in the hands of the initial purchaser of the RVMTP Shares (or certain of its affiliates), at the maximum marginal regular federal corporate income tax rate, and (y) in the case of any other holder, at the greater of (a) the maximum marginal regular federal individual income tax rate (taking into account the 3.8% Medicare contribution tax on net investment income) applicable to ordinary income or net capital gain, as applicable, or (b) the maximum marginal regular federal corporate income tax rate applicable to ordinary income or net capital gain, as applicable, in each case disregarding the effect of any state or local taxes. Any Preferred Shareholder Gross-Up will reduce the amount that would otherwise be distributable to Common Shareholders.

The “Index Rate” means the Securities Industry and Financial Markets Association (“SIFMA”) Municipal Swap Index, or such other weekly, high-grade index comprised of seven-day, tax-exempt variable rate demand notes produced by Municipal Market Data, Inc. or its successor, or as otherwise designated by the Securities Industry and Financial Markets Association; provided that if the SIFMA Municipal Swap Index is less than zero (0), the SIFMA Municipal Swap Index will be deemed to be zero (0) for purposes of the determination of the Index Rate.

For the RVMTP Shares, the Applicable Spread for a Rate Period is a percentage per annum that is based on the long-term rating most recently assigned by the applicable ratings agency to such RVMTP Shares.

With respect to the RVMTP Shares, a Failed Remarketing Spread means (a) in the case of a Failed Special Terms Period Remarketing (as defined below): (i) for so long as two or more Failed Special Terms Period Remarketings have not occurred, 0.05%, and (ii) following the second occurrence of a Failed Special Terms Period Remarketing, 0.10% multiplied by the number of Failed Special Terms Period Remarketings that have occurred after the first Failed Special Terms Period Remarketing, and (b) in the case of a Failed Early Term Redemption Date Remarketing (as defined below): (i) 0.75% for the first 59 days following the applicable Early Term Redemption Date, (ii) 1.00% for the 60th to the 89th day following such Early Term Redemption Date, (iii) 1.25% for the 90th to the 119th day following such Early Term Redemption Date, (iv) 1.50% for the 120th to the 149th day following such Early Term

[ ] | Base Prospectus 54