Dennis William Sullivan (September 28, 1882 – June 2, 1956) was a center fielder in Major League Baseball who played from 1905 through 1909 for the Washington Senators (1905), Boston Americans / Red Sox (1907–1908) and Cleveland Naps (1908–1909).

He received a great deal of playing time with Boston before Tris Speaker replaced him at center field.

His most productive season came in 1907, when he posted career-highs in games (144), batting average (.245), hits (135), runs (73), RBI (26) and on-base percentage (.315).

Traded to Cleveland in the 1908 midseason, he also played seven games for the Naps in parts of two seasons.

This biographical article relating to an American baseball outfielder born in the 1880s is a stub.