Martin Van Buren National Historic Site Boundary Adjustment Act of 2005 - Adjusts the boundary of the Martin Van Buren National Historic Site in the State of New York to include approximately 261 acres of land identified as the "Proposed Park Additions" as depicted on the "Boundary Map, Martin Van Buren National Historic Site", dated January 2005 (the map).
Authorizes the Secretary of the Interior to acquire: (1) approximately 70 acres of land and interests outside the boundary of the Site identified as "53-1-17.2" and "53-1-19.111", as depicted on the map; and (2) in order to preserve the Site's resources and scenic values, land or interests outside the Site's boundary necessary for administrative, maintenance, curatorial, or other park purposes. Revises the Site's boundary to include any such acquired land.
Allows the Secretary to acquire the lands and interests in this Act from a willing seller.