Purpose : We verified electromyogram activity during hip flexion under different pelvic rotation positions, investigated the effects of pelvic rotational position and defined the difference between males and females. Subjects : 15 healthy adults (5 male, 10 female) with a mean age of 28.8 years participated in this study. Method : We recorded surface electromyograms of the tensor fasciae latae muscle (TFL), rectus femoris muscle (RF), biceps femoris muscle (BF), semitendinosus muscle (ST), and the bilateral internal oblique muscle (OI) during flexion of the hip joint in a supine position with three different pelvis rotation conditions. Results : Males showed no significant differences at all muscle activity levels. Meanwhile, TFL muscle activities were significantly higher for females in other side rotation of the pelvis than in the pelvis neutral position (p<0.05). Moreover, opposite side of OI muscle was activated significantly highly in both side rotation position (p<0.05). Conclusion : Generally, the transverse diameter of the pelvis in females is longer than that in males. When the lower extremity is elevated in the pelvis rotation positions, the moment of force on the pelvis is thought to be higher in females. Therefore, the stabilizing muscles of the pelvis, like the OI, need to be activated isometrically in females.