Prince Saionji Kinmochi (西園寺 公望, 7 December 1849 – 24 November 1940) was a Japanese politician who served as prime minister of Japan from 1906 to 1908, and from 1911 to 1912.

As the last surviving member of the genrō, the group of senior statesmen who had directed policy during the Meiji era, he was one of the most influential voices in Japanese politics from the mid-1920s to the early 1930s.

Kinmochi was born in Kyoto as the son of Udaijin Tokudaiji Kin'ito (1821–1883), head of a kuge family of court nobility.

He took part in the climactic events of his time, the Boshin War, the revolution in Japan of 1867 and 1868, which overthrew the Tokugawa shogunate and installed the young Emperor Meiji as the (nominal) head of the government.

Saionji held the strong opinion that the nobles of the Imperial Court should seize the initiative and take part in the war.

By this time he had acquired an Imperial banner made by Iwakura Tomomi, featuring a sun and moon on a red field.

He left Japan on the SS Costa Rica with a group of thirty other Japanese students sailing to San Francisco.

Saionji arrived in France with highly reactionary views but he was influenced by Acollas (a former member of the League of Peace and Freedom) and became the most liberal of Japanese major political figures of his generation.

He made many acquaintances in France, including Franz Liszt, the Goncourt brothers, and the fellow Sorbonne student Georges Clemenceau.

In 1882, Itō Hirobumi visited Europe to research the constitutional systems of each major European country, and he asked Saionji to accompany him, as they knew each other very well.

Returning to Japan, Saionji joined the Privy Council, and served as vice president of the House of Peers.

Both his ministries were marked by continuing tension between Saionji and the powerful arch-conservative genrō, Field Marshal Yamagata Aritomo.

Saionji had to struggle with the national budget with many demands and finite resources, Yamagata sought ceaselessly the greatest expansion of the army.

Saionji's first cabinet was brought down in 1908 by conservatives led by Yamagata who were alarmed at the growth of communism and socialism, who felt the government's suppression of communists and socialists (after a parade and riots) had been insufficiently forceful.

The Taishō Crisis (so named for the newly enthroned emperor) erupted in late November 1912, out of the continuing bitter dispute over the military budget.

This was another point in which he was opposed by nationalists in the Army, who wished for the Emperor to participate in Japanese politics directly and thus weaken both parliament and the cabinet.

Saionji, when he could, chose as prime minister the president of the majority party in the Diet, but his power was always constrained by the necessity of at least the tacit consent of the army and navy.

Upon receiving news of the mutiny, Saionji fled in his car but was pursued for a great distance by a suspicious vehicle that he and his companions assumed held soldiers bent on his murder.