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 Glenelg being admitted to the seniors after one year in the B Grade (Reserves).

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

South Adelaide, Sturt also made the top (final) four teams and participated in the finals series.

This Australian rules football competition-related article is a stub.