497

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

May 5, 2016

VIA EDGAR

Securities and Exchange Commission

100 F Street, NE

Washington, DC 20549

Re: BlackRock High Yield Municipal Fund and

BlackRock National Municipal Fund,

each 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 April 29, 2016, to the Prospectus, dated October 28, 2015, for BlackRock High Yield Municipal Fund and BlackRock National Municipal Fund (the “Funds”). The purpose of the filing is to submit the 497(e) filing dated April 29, 2016 in XBRL for the Funds.

Any questions or comments on this filing should be directed to the undersigned at 212-728-8138.

Very truly yours,

/s/ Elliot J. Gluck

Elliot J. Gluck

Enclosures

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

XML

Label	Element	Value
Risk/Return:	rr_RiskReturnAbstract
Document Type	dei_DocumentType	Other
Document Period End Date	dei_DocumentPeriodEndDate	Jun. 30, 2015
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	Apr. 29, 2016
Document Effective Date	dei_DocumentEffectiveDate	Apr. 29, 2016
Prospectus Date	rr_ProspectusDate	Oct. 28, 2015

XML

Oct. 28, 2015

BlackRock Municipal Bond Fund, Inc.

BlackRock High Yield Municipal Fund

BlackRock National Municipal Fund

(each, a “Fund” and collectively, the “Funds”)

Supplement dated April 29, 2016 to the Prospectus and

Statement of Additional Information, each dated October 28, 2015

Effective June 1, 2016, the following changes are made to the Funds’ Prospectus:

Footnote 1 to each Fund’s fee 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 sections of the Prospectus entitled “Fund Overview—Key Facts About BlackRock High Yield Municipal Fund—Fees and Expenses of the Fund” and “Fund Overview—Key Facts About BlackRock National 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 1.00% 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 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. 28, 2015

Supplement [Text Block]

bmbfi_SupplementTextBlock

BlackRock Municipal Bond Fund, Inc.

BlackRock High Yield Municipal Fund

BlackRock National Municipal Fund

(each, a “Fund” and collectively, the “Funds”)

Supplement dated April 29, 2016 to the Prospectus and

Statement of Additional Information, each dated October 28, 2015

Effective June 1, 2016, the following changes are made to the Funds’ Prospectus:

Footnote 1 to each Fund’s fee 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 sections of the Prospectus entitled “Fund Overview—Key Facts About BlackRock High Yield Municipal Fund—Fees and Expenses of the Fund” and “Fund Overview—Key Facts About BlackRock National 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 1.00% 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 of an investment of $250,000 or more.

BlackRock High Yield Municipal Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

bmbfi_SupplementTextBlock

BlackRock Municipal Bond Fund, Inc.

BlackRock High Yield Municipal Fund

(each, a “Fund” and collectively, the “Funds”)

Supplement dated April 29, 2016 to the Prospectus and

Statement of Additional Information, each dated October 28, 2015

Effective June 1, 2016, the following changes are made to the Funds’ Prospectus:

Footnote 1 to each Fund’s fee 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 sections of the Prospectus entitled “Fund Overview—Key Facts About BlackRock High Yield Municipal Fund—Fees and Expenses of the Fund” and “Fund Overview—Key Facts About BlackRock National 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 1.00% 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 of an investment of $250,000 or more.

BlackRock National Municipal Fund

Risk/Return:

rr_RiskReturnAbstract

Supplement [Text Block]

bmbfi_SupplementTextBlock

BlackRock Municipal Bond Fund, Inc.

BlackRock National Municipal Fund

(each, a “Fund” and collectively, the “Funds”)

Supplement dated April 29, 2016 to the Prospectus and

Statement of Additional Information, each dated October 28, 2015

Effective June 1, 2016, the following changes are made to the Funds’ Prospectus:

Footnote 1 to each Fund’s fee 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 sections of the Prospectus entitled “Fund Overview—Key Facts About BlackRock High Yield Municipal Fund—Fees and Expenses of the Fund” and “Fund Overview—Key Facts About BlackRock National 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 1.00% 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 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. 28, 2015
Document Creation Date	dei_DocumentCreationDate	Apr. 29, 2016