[Purpose] The purpose of this study was to investigate the activation of the vastus medialis oblique muscle (VMO) and vastus lateralis muscle (VL) during squat exercise with various hip adduction loads using a pressure-biofeedback unit, and to suggest the most effective exercise method. [Subjects] We recruited 15 healthy adult females with no pain in the knee joint and no other orthopedic problems of the lower limbs. [Methods] The enrolled individuals performed four exercises (conventional squat exercise, maximal load hip adduction squat exercise, 80% hip adduction squat load exercise, 40% hip adduction load squat exercise). [Result] VMO was more active at 80% and 40% hip adduction loads than in the conventional squat and maximal loading hip adduction squat exercises. [Conclusion] We suggest using a 40%~80% hip adduction load in squat exercises for VMO strengthening in the clinical setting.