1931 WANFL season

The 1931 WANFL season was the 47th season of the Western Australian National Football League and the first under that moniker, having been called the West Australian Football League (WAFL) until 1930.

The season saw East Fremantle win its fourth consecutive premiership for the second time, having already done so between 1908 and 1911. It also saw a major revival by East Perth, who had fallen to a clear last in 1929. The Great Depression and consequent search for work saw the beginning of the first major drain of Western Australian players to powerful VFL clubs, with the loss of George Moloney to Geelong, Ron Cooper to and Keith Hough to South Melbourne, where Hough never played a single match due to the WANFL's refusal to grant the VFL Swans a clearance.

Subiaco, a power since 1924, lost star rover Johnny Leonard to country Victoria but, despite four consecutive losses mid-season, won eight straight to reach the Second-Semi and Grand Finals only to face a much larger player drain than seen so far in the WANFL.

Finals
Starting from this season, the league adopted the Page–McIntyre system of finals, in the same year as was done in the VFL. It eliminated the need for a challenge final and the uncertainty about the number of finals matches to be played, involving a fixed four finals matches exclusive of draws. This year, the first semi-final was drawn and this ensured the latest ever finish to a season, which reached as late as mid-October.