As filed with the U.S. Securities and Exchange Commission on November 12, 2013

Securities Act File No. 002-57354

Investment Company Act File No. 811-02688

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-1A

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933	x
Pre-Effective Amendment No.	¨
Post-Effective Amendment No. 53	x
and/or
REGISTRATION STATEMENT
UNDER
THE INVESTMENT COMPANY ACT OF 1940	x

Amendment No. 51

(Check appropriate box or boxes)

BLACKROCK MUNICIPAL BOND FUND, INC.

(Exact Name of Registrant as Specified in Charter)

100 Bellevue Parkway

Wilmington, Delaware 19809

(Address of Principal Executive Office)

Registrant’s Telephone Number, including Area Code (800) 441-7762

John M. Perlowski

BlackRock Municipal Bond Fund, Inc.

55 East 52^nd Street, New York, New York 10055

(Name and Address of Agent for Service)

Copies to:

Counsel for the Fund: Margery K. Neale, Esq. Willkie Farr & Gallagher LLP 787 Seventh Avenue New York, New York 10019-6099 Benjamin Archibald, Esq. BlackRock Advisors, LLC 55 East 52^nd Street New York, New York 10055

Continuous

(Approximate Date of Proposed Offering)

It is proposed that this filing will become effective:

x immediately upon filing pursuant to paragraph (b)

¨ on (date) pursuant to paragraph (b)

¨ 60 days after filing pursuant to paragraph (a)(1)

¨ on (date) pursuant to paragraph (a)(1)

¨ 75 days after filing pursuant to paragraph (a)(2)

¨ on (date) pursuant to paragraph (a)(2) of Rule 485.

If appropriate, check the following box:

¨ This post-effective amendment designates a new effective date for a previously filed post-effective amendment.

Title of Securities Being Registered: Shares of Common Stock par value, $0.10 per share.

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933 and the Investment Company Act of 1940, the Registrant certifies that it meets all the requirements for the effectiveness of this Registration Statement under Rule 485(b) under the Securities Act and it has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of New York, and the State of New York on November 12, 2013.

	BlackRock Municipal Bond Fund, Inc.
	(Registrant)
By:	/s/ JOHN M. PERLOWSKI
	(John M. Perlowski,
	President and Chief Executive Officer)

Pursuant to the requirements of the Securities Act of 1933, this Post-Effective Amendment to the Registration Statement has been signed below by the following persons in the capacities and on the dates indicated:

Signature	Title	Date
/s/ JOHN M. PERLOWSKI	President and Chief Executive Officer	November 12, 2013
(John M. Perlowski)	(Principal Executive Officer)
/s/ NEAL J. ANDREWS	Chief Financial Officer (Principal	November 12, 2013
(Neal J. Andrews)	Financial and Accounting Officer)
JAMES H. BODURTHA*	Director
(James H. Bodurtha)
BRUCE R. BOND*	Director
(Bruce R. Bond)
DONALD W. BURTON*	Director
(Donald W. Burton)
STUART E. EIZENSTAT*	Director
(Stuart E. Eizenstat)
KENNETH A. FROOT*	Director
(Kenneth A. Froot)
ROBERT M. HERNANDEZ*	Director
(Robert M. Hernandez)

JOHN F. O’BRIEN*	Director
(John F. O’Brien)
ROBERTA COOPER RAMO*	Director
(Roberta Cooper Ramo)
DAVID H. WALSH*	Director
(David H. Walsh)
FRED G. WEISS*	Director
(Fred G. Weiss)
PAUL L. AUDET*	Director
(Paul L. Audet)
LAURENCE D. FINK*	Director
(Laurence D. Fink)
HENRY GABBAY*	Director
(Henry Gabbay)

*By:	/s/ BENJAMIN ARCHIBALD	November 12, 2013
	(Benjamin Archibald, Attorney-in-Fact)

EXHIBIT INDEX

Index No.	Description of Exhibit
EX-101.INS	XBRL Instance Document
EX-101.SCH	XBRL Taxonomy Extension Schema Document
EX-101.CAL	XBRL Taxonomy Extension Calculation Linkbase
EX-101.DEF	XBRL Taxonomy Extension Definition Linkbase
EX-101.LAB	XBRL Taxonomy Extension Labels Linkbase
EX-101.PRE	XBRL Taxonomy Extension Presentation Linkbase