This study examines effects of rapid weight reduction on isokinetic maximal muscle power and muscle endurance in high school aged taekwondo players on 10 trained males. The methods of Weight reduction is selected exercise, diet, and sauna on 5% self weight. The test performed 60°/sec on isokinetic maximal muscle power and 180°/sec on muscle endurance using isokinetic machine. Variables are peak torque(PT), peak torque/body weight(FT/BW), total work(TW), Hamstring/Quadriceps ratio(H/Q ratio). The results of this study are as follows : After weight control during a week on isokinetic maximal muscle power, FT showed significant change on left knee extensor(p＜.05), PT/BW showed significant change on right and left knee extensor(p＜.05), and TW showed no significant change on knee extensor. Isokinetic maximal muscle power, FT showed significant change on right and left knee flexor(p＜.05), PT/BW showed significant change on right knee flexor(p＜.05), and TW showed significant change on right knee flexor(p＜.05). Muscle endurance, FT showed significant change on right(p＜.05) and left knee extensor(p＜.01), PT/BW showed significant change on left knee extensor(p＜.05), and TW showed no significant change on knee extensor. Muscle endurance, FT showed significant change on left knee flexor(p＜.05), PT/BW showed significant change on right and left knee flexor(p＜.05), and TW showed significant change on left knee flexor(p＜.05). H/Q ratio, showed no significant change on isokinetic maximal muscle power(60°/sec) and muscle endurance(180˚/sec). In conclusion, reduced weight through methods of exercise, diet and sauna decreased significantly on ability of isokinetic maximal muscle power and muscle endurance in taekwondo players.