1921 SAFL season

The 1921 South Australian Football League season was the 42nd season of the top-level Australian rules football competition in South Australia.

The competition expanded from seven to eight teams with being admitted to the seniors after one year in the B Grade (Reserves).

The season opened on Saturday 7 May with the opening fixture between and, and concluded on Saturday 8 October with the Grand Final, in which Minor Premiers  went on to record its 9th premiership, defeating  by 8 points.

, also made the top (final) four teams and participated in the finals series. ,, , all missed the top four. Glenelg finished winless (as they also did in next three seasons 1922–1924) to "win" the wooden spoon in its first season.