Masayoshi Ōishi (大石 昌良, Ōishi Masayoshi, born January 5, 1980) is a Japanese musician and singer-songwriter from Uwajima, Ehime. His professional music career began in 2001 as vocalist of the band Sound Schedule. Following the band's disbandment in 2006, he began a solo career, releasing his debut single "Honoka Terasu" in 2008. Sound Schedule reunited in 2011, with Ōishi returning as the band's vocalist.
Ōishi is also vocalist of the musical group OxT, led by composer Tom Hack. In 2014, Ōishi's song "Kimi Ja Nakya Dame Mitai" was used as the opening theme to the anime series Monthly Girls' Nozaki-kun, and in 2018, his song "Otomodachi Film" was used as the opening theme to the anime series Tada Never Falls in Love. He has also written songs for other artists, such as "Yōkoso Japari Park e" which was used as the opening theme to the anime series Kemono Friends.