Otto Franklin Branstetter (May 5, 1877 – August 2, 1924) was an American socialist official.

[5] In 1921, Branstetter was a lead organizer against the communist-affiliated left wing within the Socialist Party when he introduced a resolution that called for the expulsion of SPA members who supported the Communist International (Comintern).

On February 1, 1924, Branstetter submitted his resignation to the National Executive Committee, calling himself "tired and worn out."

Otto and his wife, Winnie Branstetter, married in 1899 and moved to Oklahoma in 1904.

Otto's wife, Winnie, was also a socialist organizer as well as a prominent suffragette.