Alf "Kaka" Martinsen (29 December 1911 – 23 August 1988) was a Norwegian football (soccer) player.
At the 1936 Summer Olympics he was a member of the Norwegian team, which won the bronze medal in the football tournament.
He also took part in the 1938 FIFA World Cup, but did not play a single match.
On club level he started his career in Lillestrøm-based workers' team Fram, before joining Lillestrøm SK.
He coached Lillestrøm SK from 1947 to 1950 and from 1952 to 1953.