- One People -- One Six Conspiracy
- One Sixteen Soljaz -- One To Midnight
- One-To-One -- One Voice (Pop)
- One Watt Sun -- ONE4ALL
- ONE4FIVE -- Oneironaut
- Oneironauts -- One'sy Mack
- Onethirtyeight -- Onika
- Onil -- Onkel Fisch
- Onkel Hotte's Maerchenstu -- Only Now Existing
- Only Once -- Ono Loco
- 小野正利 -- Ontuak
- O.N.U. Orchestra -- Onyx Eyes
- Onyx Olympia -- Oojami
- Ooji -- Ooze
- Ooze -- OPEE
- Open -- Open Sky Unit
- Open Skyz -- Opéra House Orchestra
- Opera IX -- Operation Ivy
- Operation Makeout -- Ophelia of the Spirits
- Ophelia Ragtime Orchestra -- Opie Ortiz
- Opie's Dream -- Opozycja
- Oppas -- Optamus