This study was conducted to investigate the effect of soybean peptide on muscle damage index and hormone (testosterone and cortisol) concentration. Subjects of this study were 23 high school male taekwondo players who had participated in regular exercise. They were randomly divided into two groups, one group took soybean peptide (S-peptide, n=13) 4 g a day for 4 weeks and the other took placebo (placebo, n=10) for the same time. We obtained blood samples before and after experiment and analyzed for CPK (Creatine phosphokinase), LDH (Lactate dehydrogenase), ALD (Aldolase), myoglobin, testosterone and cortisol. As for body composition, there was no significant difference in weight, body fat rate and LBM (lean body mass) between the S-peptide and the S-peptide group and placebo group. In CPK, LDH, ALD and myoglobin, S-peptide group was significantly lower than the placebo group and showed significant decrease before and after intaking soybean peptide (P<0.05~0.01). In the concentration of plasma testosterone, S-peptide group was increased from two weeks but not significant difference. The concentration of plasma cortisol showed significantly decrease in the S-peptide (P<0.01). These results indicate that the intake of soybean peptide have positive effect on index of muscle damage and changes of hormone concentration.