Donald Nelson Loun (born November 9, 1940) is a former Major League Baseball pitcher.

In Loun's major league debut (September 23, 1964), he pitched a 1-0 complete game shutout against the visiting Boston Red Sox, allowing just five hits and no walks.

This time he allowed eight hits, three walks, and four runs (three earned) in just four innings pitched.

His minor league career in the Washington farm system continued into the 1969 season before his retirement.

This biographical article relating to an American baseball pitcher born in the 1940s is a stub.