The Portland Blue Sox were a class-D minor league baseball team in Portland, Maine which played from 1907 to 1908 in the Maine State League and the Atlantic Association before folding. The Blue Sox were relaunched in 1919 to make up for the loss of the Portland Duffs, which folded in 1917 and played in the Eastern League. The 1919 Blue Sox were added to the New England League, but only lasted one season.
The Blue Sox' record in both the Maine State League and the Atlantic Association is unknown. Only one player who ever played for the Blue Sox made it to the majors; Cuke Barrows of Gray, Maine, who went on to play with the Chicago White Sox. Barrows played on the 1907 Blue Sox.