Ōishi, Oishi or Ooishi is a Japanese surname. Notable people with the surname include:
Hisako Ōishi (born 1936), a Japanese politician of the Democratic Party of Japan
Makoto Oishi, a Japanese wrestler, currently working for Kaientai Dojo
Masamitsu Oishi (born 1945), a Japanese politician of the Democratic Party of Japan
Nobuyuki Oishi (born 1939), a former Japanese football player
Ōishi Sadahisa (fl. 1545), a retainer of the Ogigayatsu-Uesugi branch of the Uesugi, and the builder of Takiyama Castle
Takaya Oishi (born 1972), a former Japanese football player
Tamotsu Oishi (1900–1946), a career officer in the Imperial Japanese Navy during World War II
Yoshino Ōishi (born 1944), a Japanese photographer
Ōishi Yoshio (1659–1703), the chamberlain of the Akō han in Harima Province, Japan (1679–1701)
