James Royal Mains (June 12, 1922 – March 17, 1969) was a pitcher in Major League Baseball.

[1] He attended Harvard University and played on the freshman baseball team in 1942.

That season, he pitched for the Eastern League's Utica Braves and went 0–8 with a 6.64 earned run average.

He also made one start for the Philadelphia Athletics late in the season, a complete-game loss.

[3] In 1945, Mains pitched for the American Association's Toledo Mud Hens and went 5–8, mostly in relief.