The purpose of this study is to investigate the effects of wide-squat exercise on muscle activities of vastus medialis and lateralis in a adult with Genu varum deformity. The subject, a 23 years-old male student with genu varum deformity, was performed the intervention, wide-squat exercise according to the knee joint angle, during three times a week for four weeks. After then, the changes of Q-angle and muscle activities were compared. The ratio of the vastus medialis and lateralis was changed from 30.70: 14.43 to 24.9: 30.63. Even though the wide squat exercise showed no significant change in Q-angle, that is the effective intervention for balancing the muscle activities of the vastus medialis and lateralis.