1903 Major League Baseball season

The regular season ended on September 29, with the Pittsburgh Pirates and the Boston Americans as regular season champions of the National League and American League, respectively.

The Americans defeated the Pirates, five games to three, capturing their first championship in franchise history.

National League Opening Day took place on April 16 with four teams playing, while American League Opening Day did not take place until April 20, with a doubleheader between the Philadelphia Athletics and the Boston Americans.

The National League would see its final day of the regular season on September 27, while the American League would see its final day of the season on September 29.

The 1903 season saw the following rule changes: Termed the "Battle of Ohio", the Cincinnati Reds and Cleveland Naps played an unofficial best of 11-game exhibition series after the regular season, with Cleveland winning the series six games to three.