Form 424B3 BLACKROCK MUNIASSETS

Filed Pursuant to Rule 424(b)(3)
Registration File No.: 333-288712

BLACKROCK LONG-TERM MUNICIPAL ADVANTAGE TRUST

BLACKROCK MUNIASSETS FUND, INC.

Important Information Regarding the Joint Proxy Statement/Prospectus, dated September 4, 2025 for BlackRock Long-Term Municipal Advantage Trust (“BTA”) and BlackRock MuniAssets Fund, Inc. (“MUA” or the “Acquiring Fund”)

The following changes are made to the Joint Proxy Statement/Prospectus:

The Section of the Joint Proxy Statement/Prospectus entitled “Voting Information and Requirements – Voting Requirement for Proposal 2: The Issuance of Acquiring Fund Common Shares” is deleted in its entirety and replaced with the following information:

 Voting Requirement for Proposal 2: The Issuance of Acquiring Fund Common Shares

All other references in the Joint Proxy Statement/Prospectus and the accompanying exhibits referencing the vote requirement for shareholders to approve Proposal 2 are hereby revised and restated to reflect the vote requirement stated in the table above.