497

787 Seventh Avenue New York, NY 10019-6099 Tel: 212 728 8000 Fax: 212 728 8111

March 5, 2019

VIA EDGAR

Securities and Exchange Commission

100 F Street, NE

Washington, DC 20549

Re: BlackRock Short-Term Municipal Fund, a series of BlackRock Municipal Bond Fund, Inc.

(File No. 002-57354 and File No. 811-02688)

Ladies and Gentlemen:

On behalf of BlackRock Municipal Bond Fund, Inc. and pursuant to Rule 497(e) under the Securities Act of 1933, as amended, attached for filing are exhibits containing interactive data format risk/return summary information that mirrors the risk/return summary information in a supplement, dated February 11, 2019, to the Prospectus, dated October 26, 2018, for BlackRock Short-Term Municipal Fund (the “Fund”). The purpose of the filing is to submit the 497(e) filing dated February 11, 2019 in XBRL for the Fund.

Any questions or comments on this filing should be directed to the undersigned at (212) 728-8955.

Very truly yours,

/s/ Bissie K. Bonner

Bissie K. Bonner

Enclosures

cc: Benjamin Archibald, Esq., BlackRock Advisors, LLC

Elliot J. Gluck, Esq., Willkie Farr & Gallagher LLP

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	497
Document Period End Date	dei_DocumentPeriodEndDate	Jun. 30, 2018
Registrant Name	dei_EntityRegistrantName	BLACKROCK MUNICIPAL BOND FUND, INC.
Central Index Key	dei_EntityCentralIndexKey	0000225635
Amendment Flag	dei_AmendmentFlag	false
Document Creation Date	dei_DocumentCreationDate	Feb. 11, 2019
Document Effective Date	dei_DocumentEffectiveDate	Feb. 11, 2019
Prospectus Date	rr_ProspectusDate	Oct. 26, 2018
Entity Inv Company Type	dei_EntityInvCompanyType	N-1A

XML

Oct. 26, 2018

BLACKROCK MUNICIPAL BOND FUND, INC.

BlackRock Short-Term Municipal Fund

(the “Fund”)

Supplement dated February 11, 2019 to the Summary Prospectus and the Prospectus for Investor A, Investor C and Institutional Shares of the Fund and the Statement of Additional Information of the Fund, each dated October 26, 2018, as supplemented to date

Effective March 18, 2019, with respect to Investor A shares of the Fund, BlackRock has reduced the contingent deferred sales charge (“CDSC”), shortened the CDSC holding period, and lowered the threshold at which such shares may be purchased at net asset value. Shareholders who purchased Investor A shares of the Fund prior to the implementation of these changes shall be subject to the terms of the CDSC, holding period, and threshold in effect at the time of purchase. Accordingly, effective March 18, 2019, the following changes are made to the Fund’s Summary Prospectus and Prospectus, as applicable:

Footnote 1 to the Fund’s fee and expense table relating to the “Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)” for Investor A Shares in the section of the Summary Prospectus entitled “Key Facts About BlackRock Short-Term Municipal Fund — Fees and Expenses of the Fund” and the section of the Prospectus entitled “Fund Overview — Key Facts About BlackRock Short-Term Municipal Fund — Fees and Expenses of the Fund” is deleted in its entirety and replaced with the following:

¹  A contingent deferred sales charge (“CDSC”) of 0.25% is assessed on certain redemptions of Investor A Shares made within 9 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $100,000 or more. With respect to shares purchased prior to March 18, 2019, a CDSC of 0.50% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $250,000 or more.

XML

Label

Element

Value

Risk/Return:

rr_RiskReturnAbstract

Registrant Name

dei_EntityRegistrantName

BLACKROCK MUNICIPAL BOND FUND, INC.

Prospectus Date

rr_ProspectusDate

Oct. 26, 2018

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

BLACKROCK MUNICIPAL BOND FUND, INC.

BlackRock Short-Term Municipal Fund

(the “Fund”)

Supplement dated February 11, 2019 to the Summary Prospectus and the Prospectus for Investor A, Investor C and Institutional Shares of the Fund and the Statement of Additional Information of the Fund, each dated October 26, 2018, as supplemented to date

Effective March 18, 2019, with respect to Investor A shares of the Fund, BlackRock has reduced the contingent deferred sales charge (“CDSC”), shortened the CDSC holding period, and lowered the threshold at which such shares may be purchased at net asset value. Shareholders who purchased Investor A shares of the Fund prior to the implementation of these changes shall be subject to the terms of the CDSC, holding period, and threshold in effect at the time of purchase. Accordingly, effective March 18, 2019, the following changes are made to the Fund’s Summary Prospectus and Prospectus, as applicable:

Footnote 1 to the Fund’s fee and expense table relating to the “Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)” for Investor A Shares in the section of the Summary Prospectus entitled “Key Facts About BlackRock Short-Term Municipal Fund — Fees and Expenses of the Fund” and the section of the Prospectus entitled “Fund Overview — Key Facts About BlackRock Short-Term Municipal Fund — Fees and Expenses of the Fund” is deleted in its entirety and replaced with the following:

¹  A contingent deferred sales charge (“CDSC”) of 0.25% is assessed on certain redemptions of Investor A Shares made within 9 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $100,000 or more. With respect to shares purchased prior to March 18, 2019, a CDSC of 0.50% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $250,000 or more.

BlackRock Short-Term Municipal Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement to Prospectus [Text Block]

rr_SupplementToProspectusTextBlock

BLACKROCK MUNICIPAL BOND FUND, INC.

BlackRock Short-Term Municipal Fund

(the “Fund”)

Supplement dated February 11, 2019 to the Summary Prospectus and the Prospectus for Investor A, Investor C and Institutional Shares of the Fund and the Statement of Additional Information of the Fund, each dated October 26, 2018, as supplemented to date

Effective March 18, 2019, with respect to Investor A shares of the Fund, BlackRock has reduced the contingent deferred sales charge (“CDSC”), shortened the CDSC holding period, and lowered the threshold at which such shares may be purchased at net asset value. Shareholders who purchased Investor A shares of the Fund prior to the implementation of these changes shall be subject to the terms of the CDSC, holding period, and threshold in effect at the time of purchase. Accordingly, effective March 18, 2019, the following changes are made to the Fund’s Summary Prospectus and Prospectus, as applicable:

Footnote 1 to the Fund’s fee and expense table relating to the “Maximum Deferred Sales Charge (Load) (as percentage of offering price or redemption proceeds, whichever is lower)” for Investor A Shares in the section of the Summary Prospectus entitled “Key Facts About BlackRock Short-Term Municipal Fund — Fees and Expenses of the Fund” and the section of the Prospectus entitled “Fund Overview — Key Facts About BlackRock Short-Term Municipal Fund — Fees and Expenses of the Fund” is deleted in its entirety and replaced with the following:

¹  A contingent deferred sales charge (“CDSC”) of 0.25% is assessed on certain redemptions of Investor A Shares made within 9 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $100,000 or more. With respect to shares purchased prior to March 18, 2019, a CDSC of 0.50% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $250,000 or more.

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Registrant Name	dei_EntityRegistrantName	BLACKROCK MUNICIPAL BOND FUND, INC.
Prospectus Date	rr_ProspectusDate	Oct. 26, 2018
Document Creation Date	dei_DocumentCreationDate	Feb. 11, 2019