Seiyukai (sā´yōōkī´), Japanese political party, founded in 1900. It was derived, via the Kenseito (see Minseito) from the Jiyuto, organized by Taisuke Itagaki in 1881. Under the astute political leadership of Takashi Hara, it was the most powerful party in Japan from 1900 to 1921. Hirobumi Ito was its first president, and Kimmochi Saionji its second, but these great statesmen were more powerful in their own right than as party leaders. The first real party cabinet, marking the decline of the old genro oligarchy, was formed by Takashi Hara in 1918. Party governments prevailed from 1924 to 1932, the Seiyukai cabinets of Giichi Tanaka (1927–29) and Ki Inukai (1931–32) alternating with Minseito governments. After this the influence of political parties steadily declined as that of the militarists increased. Japanese parties have been based more on factionalism and personal loyalty than on divisions of principle. The Seiyukai was generally conservative and acceded to bureaucratic and military control more willingly than the Minseito. After World War II, the Seiyukai reappeared, under the leadership of Kijuro Shidehara, as the Progressive party, the most conservative major political party in postwar Japan. The Progressives were later absorbed into the business-oriented Liberal Democratic party. The Seiyukai was traditionally identified with the Mitsui financial interests.
See P. Duus, Party Rivalry and Political Change in Taishō Japan (1968).