Ryuichi Doi (土肥 隆一 Doi Ryūichi, born February 11, 1939) is a Japanese politician serving in the House of Representatives in the Diet (national legislature) as a member of the Democratic Party of Japan. He was born in Seoul during the time Korea was occupied by Japan. He attended Tokyo Union Theological Seminary, earning a master's degree. In 1990 he was elected for the first time as a member of the Japan Socialist Party.