As a new concept of resistive exercise, isokinetic exercise was developed during the early 1950's. In isokinetic exercise, the subject works at a fixed speed against variable and totally accommodating resistance. The isokinetic equipment has been used widely as a therapeutic modality in clinical setting, as a training and testing device for sports practicians, and as a method for scientific examination of post -operative status of muscles and joint function for orthopedists. In order to acquire the isokinetic normative data of the knee for clinical use, we examined the flexor and extensor muscle force of the knee joint in 160 subjects with Cybex II. The results were as follows; 1. Mean values of extensor strength were 76.04 ft.-1bs in right knee 75.45 ft.-lbs in left knee, 78.42 ft.-1bs in dominent hand side leg 73.84 ft.-1bs in non-dominent hand side leg, and 82.52 ft.-1bs in dominent leg 71.93 ft.-lbs in non-dominent leg. 2. Sex difference of extensor strength were 95.13 ft.-lbs in male 55.98 ft.-1bs in female, and that of flexor strength were 54.90 ft.-1bs in male 33.68 ft.-1bs in female. 3. Mean of position angle of maximal torque were between 58° and 65° for extensors, 35° and 45° for flexors. 4. Mean of total range of motion at working isokinetically with 60°/sec speed was 99°. 5. Mean values of extensor power were 54.43 ft.-1bs in male 30.63 ft.-lbs in female, and that of flexor power were 35.99 ft.-1bs in male 22.42 ft.-1bs in female. 6. Strength and power decreased as ages getting old, and there was significant diminish between 4th decade and 5th decade. 7. Power endurance had more difference when it was compared with occupation. Mean value of power endurance was between 12 times and 18 times.