Prospectus Certification by Investment Company (Form 497J)

May 4, 2026

VIA ELECTRONIC FILING

Securities and Exchange Commission

100 F Street, N.E.

Washington, D.C. 20549

Attention: Division of Investment Management

RE: iShares U.S. Aggregate Bond Index Fund, a series of BlackRock Funds III

Post-Effective Amendment No. 410 to the Registration Statement on Form N-1A

(Securities Act File No. 33-54126, Investment Company Act File No. 811-07332).

Ladies and Gentlemen:

Pursuant to Rule 497(j) under the Securities Act of 1933, as amended (the "1933 Act"), BlackRock Funds III (the "Registrant"), on behalf of its series iShares U.S. Aggregate Bond Index Fund (the "Fund"), hereby certifies that:

(1) the form of Prospectuses and Statement of Additional Information that would have been filed pursuant to Rule 497(c) under the 1933 Act would not have differed from that contained in Post-Effective Amendment No. 410 to the Registration Statement on Form N-1A of the Registrant with respect to the Fund; and

(2) the text of Post-Effective Amendment No. 410 to the Registration Statement on Form N-1A of the Registrant with respect to the Fund was filed electronically with the Securities and Exchange Commission on April 28, 2026.