O
- Mike O'Berry
- Buck O'Brien
- Jack O'Brien
- Syd O'Brien
- Tommy O'Brien
- Lefty O'Doul
- Troy O'Leary
- Bill O'Neill
- Emmett O'Neill
- Steve O'Neill
- Frank O'Rourke
- Frank Oberlin
- José Offerman
- Ben Oglivie
- Tomo Ohka
- Bob Ojeda
- Hideki Okajima
- Len Okrie
- John Olerud
- Darren Oliver
- Gene Oliver
- Joe Oliver
- Tom Oliver
- Hank Olmsted
- Karl Olson
- Marv Olson
- Ted Olson
- Steve Ontiveros
- George Orme
- David Ortiz
- Luis Ortiz
- Dan Osinski
- Harry Ostdiek
- Fritz Ostermueller
- Johnny Ostrowski
- Marv Owen
- Mickey Owen
- Spike Owen
- Frank Owens
Read more about this topic: Boston Red Sox All-time Roster