The purpose of this study was to investigate the effect of soybean peptide on antioxidant enzymes, cortisol hormone and inflammatory cytokine levels. 19 high school male judo athletes participated in the experiments. They were randomly divided into two groups, one group took soybean peptide (S-peptide, n=10) 4 g a day for 4 weeks and the other group placebo (placebo group, n=9) for the same time. Blood samples were collected before intake, after 2 weeks intake and 4 weeks intake and these were analyzed for total antioxidant status (TAS), catalase (CAT), levels of cortisol hormone, tumor necrosis factor-alpha (TNF-${alpha}$) and interleukin-6 (IL-6). As a result, the S-peptide group was significantly increased in TAS and CAT (P<0.05). The malondialdehyde (MDA) levels showed decrease after soybean peptide intake but there was no significant difference. In the levels of plasma cortisol which reflect stress status, there was significantly decreased in the S-peptide and placebo group after 4 weeks (P<0.05). There were significant decreases of TNF-${alpha}$ and IL-6 after 4 weeks in S-peptide group (P<0.05). These results suggest that the intake of soybean peptide can activate antioxidant defenses and decrease exercise-induced oxidative stress.