The 2003 American Le Mans Series season was the fifth season for the IMSA American Le Mans Series, and the 33rd overall season of the IMSA GT Championship. It was a series for Le Mans Prototypes (LMP) and Grand Touring (GT) race cars divided into 4 classes: LMP900, LMP675, GTS, and GT. It began March 15, 2003, and ended October 18, 2003, after nine races.
Dyson Racing's overall win at Sonoma Raceway was the first time in ALMS history that the overall win was captured by a vehicle not from the LMP900 class.