Francis Xavier "Big Jeff" Pfeffer (March 31, 1882 – December 19, 1954) was an American Major League pitcher from 1905 to 1911.

He made his MLB debut on April 15, 1905 for the Chicago Cubs and had a 4-4 record for them that season.

He finished second in the National League that season in complete games and strikeouts.

Early the following season, Pfeffer pitched a no-hitter on May 8, 1907, with the Boston Doves defeating Cincinnati 6-0.

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