The relationship between the thigh muscle composition and the sprinting performance was investigated in 11 male adult sprinters (age/20.8±0.9 yrs, 100 m sprint time/11.20±0.33 sec). Axial images of the thigh muscle were taken by magnetic resonance imaging (MRI) at upper (70%) and middle (50%) position in femur. From these images, cross-sectional areas (CSA) of the quadriceps femoris, the hamstring and the adductor muscles were measured. The results of the regression analysis showed significant correlations between 100 m sprint time and both CSA of adductor and hamstring muscles at 70% position (r=-0.72 and r=-0.67, respectively). There were no significant correlations between 100 m sprint time and CSA of adductor or hamstring muscles at 50% position, and neither quadriceps femoris mudcles at 70 nor 50% positions. These results suggest that greater muscle volume of hamstring and adductor at upper position affect sprinting performance.