The 2003 Sirius 400 was the 15th stock car race of the 2003 NASCAR Winston Cup Series season and the 35th iteration of the event. The race was held on Sunday, June 15, 2003, before a crowd of 160,000 in Brooklyn, Michigan, at Michigan International Speedway, a two-mile (3.2 km) moderate-banked D-shaped speedway. The race took the scheduled 200 laps to complete. At race's end, Kurt Busch of Roush Racing would make adjustments at the end of the race to pass Hendrick Motorsports driver Jeff Gordon on lap 177, and hold off Bobby Labonte of Joe Gibbs Racing to win his seventh career NASCAR Winston Cup Series win and his third of the season.^[1] Labonte and Gordon would fill out the podium, finishing second and third, respectively.

The race was held at Michigan International Speedway, a two-mile (3.2 km) moderate-banked D-shaped speedway located in Brooklyn, Michigan. The track is used primarily for NASCAR events. It is known as a "sister track" to Texas World Speedway as MIS's oval design was a direct basis of TWS, with moderate modifications to the banking in the corners, and was used as the basis of Auto Club Speedway. The track is owned by International Speedway Corporation. Michigan International Speedway is recognized as one of motorsports' premier facilities because of its wide racing surface and high banking (by open-wheel standards; the 18-degree banking is modest by stock car standards).

Qualifying was held on Friday, June 13, at 3:05 PM EST. Each driver would have two laps to set a fastest time; the fastest of the two would count as their official qualifying lap.^[3] Positions 1-36 would be decided on time, while positions 37-43 would be based on provisionals. Six spots are awarded by the use of provisionals based on owner's points. The seventh is awarded to a past champion who has not otherwise qualified for the race. If no past champ needs the provisional, the next team in the owner points will be awarded a provisional.^[7]

Bobby Labonte of Joe Gibbs Racing would win the pole, setting a time of 37.822 and an average speed of 190.365 miles per hour (306.363 km/h).^[8]

Jimmy Spencer would blow an engine in the session. He was forced to use a provisional.^[9]

Two drivers would fail to qualify: Mike Skinner and Larry Foyt.