Ōishi Masami (大石 正巳, 26 May 1855 – 12 July 1935) was a politician and cabinet minister in the pre-war Empire of Japan. Ōishi was a native of Tosa Province (modern-day Kōchi Prefecture), where his father was a samurai in the service of Tosa Domain. In 1873, he joined with Itagaki Taisuke and became an important member of the Freedom and People's Rights Movement. He became one of the leaders of the Jiyūtō political party in 1881. However, he had a falling out with Itagaki in 1882 and left the party. He subsequently joined with Gotō Shōjirō’s daidō danketsu (coalition) movement in 1887. In 1892, he was appointed to the Japanese legation in Seoul, Korea. He was back in Japan by 1896, and was one of the founding members of the Shimpotō political party. Under the short-lived 1st Ōkuma Shigenobu