Toru (山下 亨) Yamashita Tōru, born December 7, 1988 in Osaka is the leader and guitarist of the group. He also contributes some vocals. He was previously a member of the hip-hop dance group Heads with Ryota.
Taka (森田 貴寬) Morita Takahiro, born April 17, 1988 in Tokyo is the main vocalist of the group. Prior to debuting with One Ok Rock, he was a member of the boy band NEWS. He is the son of singers Shinichi Mori and Masako Mori.
Ryota (小浜 良太) Kohama Ryōta, born September 4, 1989 in Osaka is the bassist of the group. He was also previously a member of the hip-hop dance group Heads with Toru.
Tomoya (神吉 智也) Kanki Tomoya, born June 27, 1987 in Hyogo is the drummer of the group.
Alex (鬼澤アレクサンダー礼門) Onizawa Alexander Reimon, born March 19, 1988 in San Francisco was lead guitarist of the group along with rhythm guitarist and vocalist Toru, until he left in May 2009 after being arrested on charges of groping.
Tomo (小柳友) Koyanagi Yuu, born August 29, 1988 in Tokyo was the original drummer of the group since before their official debut. He left the band in June 2006 to follow an acting career.