Ōishi, Oishi or Ooishi is a Japanese surname. Notable people with the surname include:

, Japanese baseball player , Japanese politician of the Democratic Party of Japan , Japanese professional wrestler , Japanese politician of the Democratic Party of Japan , former Japanese football player , Japanese footballer , retainer of the Ogigayatsu-Uesugi branch of the Uesugi, and the builder of Takiyama Castle , Japanese shogi player , career officer in the Imperial Japanese Navy during World War II , Japanese footballer , Japanese swimmer , Japanese photographer , the chamberlain of the Akō han in Harima Province, Japan (1679–1701), known as the leader of the forty-seven rōnin

Fictional characters Hisako Ōishi, a Japanese schoolteacher in the 1952 novel Twenty-Four Eyes and the 1954 film adaptation of the same name Noriko Ōishi, a central character in the 2023 film Godzilla Minus One