1921 Southern Intercollegiate Athletic Association football season

The 1921 Southern Intercollegiate Athletic Association football season was the college football games played by the member schools of the Southern Intercollegiate Athletic Association as part of the 1921 college football season.

The season began on September 23 with conference member Chattanooga visiting Athens. Conference play began on September 24 with Alabama defeating Howard.

Centre, Georgia Tech, Georgia, and Vanderbilt can all claim Southern championships. Centre and Georgia Tech both posted unblemished conference records. Georgia and Vanderbilt tied each other in their contest deciding a champion.

This is the last year before many major programs move to the Southern Conference.

Regular season
SIAA teams in bold.

All-Americans

 * E – Red Roberts, Centre (WC-1; FW-2 [g]; JV-3; MM-2)
 * E – Owen Reynolds, Georgia (FW-3)
 * G – Puss Whelchel, Georgia (WC-3)
 * QB – Bo McMillin, Centre (FW-1; WC-2; LP-1 [hb]; BE-2; JV-2; MM-1; NB-1)
 * HB – Red Barron, Georgia Tech (JV-3)
 * FB – Judy Harlan, Georgia Tech (WC-3; FW-3)

All-Southern team
The following includes the composite All-Southern eleven awarded gold badges and formed by 30 sports writers culled by the Atlanta Constitution and Atlanta Journal.