The 1921 College Football All-Southern Team consists of American football players selected to the College Football All-Southern Teams selected by various organizations for the 1921 Southern Intercollegiate Athletic Association football season. This was the last year before many schools left the Southern Intercollegiate Athletic Association (SIAA) for the Southern Conference (SoCon).
Centre posted the SIAA's best record and upset Harvard 6–0. Georgia Tech was also undefeated in conference play, as were Georgia and Vanderbilt, the latter two posting one tie against the other. Vanderbilt was the only one to remain undefeated overall, and were selected as a national champion retroactively by selector Clyde Berryman.
The composite All-Southern eleven awarded gold badges and formed by 30 sports writers culled by the Atlanta Constitution and Atlanta Journal included:
Bo McMillin was the only unanimous choice for the composite selection. Caton and Staton were picked out of the ties due to having the most votes at multiple positions.
Bold = Composite selection
* = Consensus All-American
† = Unanimous selection
C = Received votes for a composite All-SIAA eleven selected by 30 sports writers and culled by the Atlanta Constitution and Atlanta Journal. Each of the composite eleven selected were presented with gold football badges.