Mathias John Zeiser (sometimes spelled Zieser) (September 25, 1888 – June 10, 1942) was a professional baseball pitcher.

He appeared in two games in Major League Baseball for the Boston Red Sox during the 1914 season, both as a relief pitcher.

He was born and died in Chicago, Illinois.

In a two-game career, Zeiser posted a 1.80 earned run average with eight walks in 10 innings pitched.

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