SIDLEY AUSTIN LLP 787 SEVENTH AVENUE NEW YORK, NY 10019 (212) 839 5300 (212) 839 5599 FAX   BEIJING BOSTON BRUSSELS CENTURY CITY CHICAGO DALLAS GENEVA   FOUNDED 1866   HONG KONG HOUSTON LONDON LOS ANGELES MUNICH NEW YORK PALO ALTO   SAN FRANCISCO SHANGHAI SINGAPORE SYDNEY TOKYO WASHINGTON, D.C.

October 26, 2016

VIA EDGAR

U.S. Securities and Exchange Commission

100 F Street, N.E.

Washington, D.C. 20549

Attention: Division of Investment Management

Re: BlackRock International Index Fund and BlackRock Small Cap Index Fund, each

a series of BlackRock Index Funds, Inc.

(Securities Act File No. 333-15265, Investment Company Act File No. 811-7899)

Ladies and Gentlemen:

On behalf of BlackRock Index Funds, Inc., attached for filing are exhibits containing interactive data format risk/return summary information that mirrors the risk/return summary information in the Prospectuses dated August 1, 2016 (as amended October 5, 2016) of BlackRock International Index Fund and BlackRock Small Cap Index Fund (the “Funds”), as filed pursuant to Rule 497(e) under the Securities Act of 1933 on October 5, 2016 (the “497 Filing”). The purpose of this filing is to submit the 497 Filing in XBRL for the Funds.

Any questions or comments on the 497 Filing should be directed to the undersigned at (212) 839-8615.

Very truly yours,

/s/ Jesse C. Kean

Jesse C. Kean

cc:    Benjamin Archibald

John A. MacKinnon

Sidley Austin (NY) LLP is a Delaware limited liability partnership doing business as Sidley Austin LLP and practicing in affiliation with other Sidley Austin partnerships.