BLACKROCK INDEX FUNDS, INC.

BlackRock Small Cap Index Fund

(the “Fund”)

Supplement dated April 5, 2017

to the Fund’s Summary Prospectus dated October 5, 2016 and Prospectus

and Statement of Additional Information (“SAI”), each dated August 1, 2016 (as amended October 5, 2016)

Effective June 19, 2017, the Fund will change its name to iShares Russell 2000 Small-Cap Index Fund. Accordingly, effective June 19, 2017, references to the Fund’s name in the Fund’s Summary Prospectus, Prospectus and SAI are changed to reflect the new Fund name.

Shareholders should retain this Supplement for future reference.

PR2SAI-INDX3-0417SUP