O
- Martin O'Donnell – Halo series
- Hisayoshi Ogura – Zuntata sound team, Darius, Darius II (also called Sagaia), Darius Gaiden, G Darius, Night Striker, The Ninja Warriors, Rainbow Islands (Sega Master System port, with Tadashi Kimijima)
- Haruo Ohashi – Wild Guns (with Hiroyuki Iwatsuki), Mighty Morphin Power Rangers: The Movie (SNES, with Hiroyuki Iwatsuki), Mighty Morphin Power Rangers: The Fighting Edition (with Hiroyuki Iwatsuki)
- Asuka Ota – The Legend of Zelda: Four Swords Adventures, Yoshi Touch & Go, New Super Mario Bros.
- Tomoya Ohtani – Sonic Heroes, Sonic the Hedgehog, Sonic Unleashed
- Soyo Oka – SimCity, Super Mario Kart (with Koji Kondo and Taro Bando)
- Hiroshi Okubo – Ace Combat series, Katamari Damacy
- Masanori Oodachi – Super Castlevania 4 (With Sotaro Tojima, also known as Souji Taro)
- Kenichi Ōkuma – Melty Lancer series, Ring ni Kakero (video game)
- Shinji Orito – Dōsei, Moon., One: Kagayaku Kisetsu e, Kanon, Air, Clannad, Tomoyo After: It's a Wonderful Life, Little Busters!, Rewrite
- Michiru Oshima – Genghis Khan II: Clan of the Grey Wolf, ICO
- OverClocked ReMix – Super Street Fighter II Turbo HD Remix
- Waichiro Ozaki – Mitsumete Knight R, Emphemeral Fantasia, Metal Gear Solid: The Twin Snakes
Read more about this topic: List Of Video Game Musicians