Southern United F.C. was an English football club based in the Nunhead area of London.
Established in 1905, the club entered teams into Division Two of the Southern League and Division One of the London League. They withdrew from the Southern League at the end of the 1905–06 season, and from the London League during the 1906–07 season.
Professional players at the club included Frederick Mearns, Michael Good and former England international Fred Spiksley.