Tetsu Katayama (片山 哲 Katayama Tetsu, July 28, 1887 - May 30, 1978) was a Japanese politician and the 46th Prime Minister from May 24 1947 to March 10 1948.

He was born in Tanabe, Wakayama Prefecture, and attended Tokyo Imperial University. After graduating, he opened a law office in a rented YMCA dormitory, and worked as an attorney. Katayama joined the Japan Socialist Party and was elected to the House of Representatives, representing Kanagawa Prefecture, in 1930. He became known as a leader of the "social democratic wing" of the party, and joined Abe Iso and Nishio Suehiro in opposing the expulsion of Saito Takao .

In 1945, Katayama became secretary general and committee chairman of the party. Following the 1947 elections, in which the Socialist Party came in first, Katayama formed a coalition government with the Democratic Party and the Citizens' Cooperation Party . However, the influence of left-wing socialists such as Suzuki Mosaburo forced Katayama to resign early in his term.

After his resignation, Katayama became a member of the Democratic Socialist Party and advocated the maintenance of the pacifist constitution, election reform, and formation of a global commonwealth.