U-26 may refer to one of the following German submarines:
- SM U-26, was a Type U 23 submarine launched in 1913 and that served in the First World War; torpedoed Russian armored cruiser Pallada in October 1914; sunk in August/September 1915
- German submarine U-26 (1936), a Type IA submarine that served in the Second World War until scuttled on 1 July 1940
- German submarine U-26 (S175), a Type 206 submarine of the Bundesmarine that was launched in 1974 and removed from service in 2005