Nintendo DS - O
- O.M.G. 26 - Our Mini Games
- Obscure - Dark Aura
- Obscure - the Aftermath
- Ochaken no Daibouken
- Ochaken no Heya DS 3
- Office
- Offshore Tycoon
- Okamiden
- One Piece - Gear Spirit
- One Piece - Gigant Battle
- One Piece - Gigant Battle 2 - Shinsekai
- One Piece - Gigant Battle!
- Ontamarama
- Open Season
- Operation - Vietnam
- Orcs and Elves
- Oscar in Toyland
- Oscar in Toyland 2
- Ossu! Tatakae! Ouendan!
- Ouran Koukou Host Club DS
- Over the Hedge
- Over the Hedge - Hammy Goes Nuts
- Overlord Minions
- Oyaku de Asoberu DS Ehon - Ukkari Penelope