Players — U
- Edwin Uceta 2021–2025
- Jimmy Uchrinscko 1926–1926
- Bob Uecker 1962–1967
- Koji Uehara 2009–2017
- Erich Uelmen 2022–2023
- Dan Uggla 2006–2015
- Luis Ugueto 2002–2003
- Frenchy Uhalt 1934–1934
- Bob Uhl 1938–1940
- Ted Uhlaender 1965–1972
- George Uhle 1919–1936
- Maury Uhler 1914–1914
- uhler01 1900–1900
- Charlie Uhlir 1934–1934
- Jerry Ujdur 1980–1984
- Mike Ulicny 1945–1945
- Scott Ullger 1983–1983
- Sandy Ullrich 1944–1945
- Frank Ulrich 1925–1927
- George Ulrich 1892–1896
- Arnold Umbach 1964–1966
- Jim Umbarger 1975–1978
- Jim Umbricht 1959–1963
- Tom Umphlett 1953–1955
- Vern Underhill 1927–1928
- Duane Underwood 2018–2023
- Eli Underwood 1937–1937
- Fred Underwood 1894–1894
- Pat Underwood 1979–1983
- Tom Underwood 1974–1984
- under01 1932–1932
- Bob Unglaub 1904–1910
- Tim Unroe 1995–2000
- Al Unser 1942–1945
- Del Unser 1968–1982
- Woody Upchurch 1935–1936
- Bill Upham 1915–1918
- John Upham 1967–1968
- Jerry Upp 1909–1909
- Dixie Upright 1953–1953
- Cecil Upshaw 1966–1975
- Willie Upshaw 1978–1988
- B. J. Upton 2004–2016
- Bill Upton 1954–1954
- Justin Upton 2007–2022
- Tom Upton 1950–1952
- Jack Urban 1957–1959
- Luke Urban 1927–1928
- urban01 1945–1945
- Tom Urbani 1993–1996
- Billy Urbanski 1931–1937
- Ugueth Urbina 1995–2005
- Lino Urdaneta 2004–2007
- Jose Urena 2015–2025
- Richard Urena 2017–2019
- Julio Urias 2016–2023
- Luis Urias 2018–2025
- Ramon Urias 2020–2025
- Abner Uribe 2023–2025
- Jose Uribe 1984–1993
- Juan Uribe 2001–2016
- Jose Urquidy 2019–2025
- John Urrea 1977–1981
- Henry Urrutia 2013–2015
- Gio Urshela 2015–2025
- Lon Ury 1903–1903
- Bob Usher 1946–1957
- Dutch Ussat 1925–1927
- Chase Utley 2003–2018
- Naoyuki Uwasawa 2024–2024