The 1909 Boston Red Sox season was the ninth season in the franchise's Major League Baseball history. The Red Sox finished third in the American League (AL) with a record of 88 wins and 63 losses, 9+1⁄2 games behind the Detroit Tigers. The team played its home games at Huntington Avenue Grounds.

The 1909 Detroit Tigers won the American League pennant with a record of 98–54, but lost to the Pittsburgh Pirates in the 1909 World Series, 4 games to 3. The season was their ninth since they were charter members of the American League in 1901. It was the third consecutive season in which they won the pennant but lost the World Series. Center fielder Ty Cobb won the Triple Crown and pitcher George Mullin led the league in wins (29) and winning percentage (.784).