Mark Alan Williamson (born July 21, 1959) is an American former professional baseball player who pitched in the Major Leagues from 1987 to 1994. He played for the Baltimore Orioles. On April 29, 1988, Williamson pitched 6 shutout innings to help the Orioles defeat the White Sox 9-0. The victory snapped the Orioles' 21-game losing streak that started the 1988 season. On July 13, 1991, he pitched a no-hitter along with Bob Milacki, Mike Flanagan, and Gregg Olson against the Oakland Athletics.