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- Fran O'Brien (1966–1968)
- Jack O'Brien (1954–1956)
- Mel Odelli (1945)
- Henry Odom (1983)
- Pat O'Donahue (1953–1955)
- Neil O'Donnell (1990–1995)
- John Oehler (1933–1934)
- John Oelerich (1938)
- A.J. Ofodile (1995)
- Chukky Okobi (2001–2006)
- Chris Oldham (1995–1999)
- Ray Oldham (1978)
- Dan O'Leary (2002)
- Stan Olejniczak (1935)
- Oliver (1935)
- Clarence Oliver (1969–1970)
- Jerry Olsavsky (1989–1997), (2010–2011)
- Ryan Olson (1998)
- Al Olszewski (1945)
- Joe O'Malley (1955–1956)
- Bob O'Neil (1956–1957)
- Dennis Onkotz (1971)
- David Opfar (1987)
- Tony Orlandini (1998–2000)
- Bo Orlando (1998)
- Kenneth Ormiston (1948–1950)
- Jimmy Orr (1958–1960)
- Chuck Ortmann (1951–1952)
- Terry O'Shea (1989–1990)
- Paul Oswald (1987)
- Darrick Owens (1992)
Read more about this topic: List Of Pittsburgh Steelers Players