The 21st Independent Mixed Brigade (21st IMB) was an infantry brigade of the Imperial Japanese Army raised during World War II. Formed in January 1941 in Osaka, Japan, the brigade consisted of a single infantry regiment and support elements. It undertook occupation duties in Indochina before being sent to Malaya and then Rabaul. In late 1942, the brigade was sent to take part in the Battle of Buna–Gona in New Guinea. It was withdrawn to Rabaul, and then Japan, in June 1943. Elements of the brigade were converted into other formations and the formation ceased to exist in July 1943.