The 1903 major league baseball season began on April 16, 1903. The regular season ended September 29, with the Pittsburgh Pirates and the Boston Americans as regular season champions of the National League and American League, respectively. The postseason began with Game 1 of the first modern World Series on October 1 and ended with Game 8 on October 13. The Americans defeated the Pirates, five games to three.

The 1903 Cleveland Naps season was the third Major League Baseball season for the Cleveland American League team. After two seasons as the Bluebirds or Blues and also being called the Bronchos in 1902, beginning with the 1903 season, the team was called the Naps in honor of star second baseman Nap Lajoie. The team finished third in the league with a record of 77–63, 15 games behind the Boston Americans.