This study was undertaken to investigate the effects of progressive resistance-training (PRT) on plasma oxidative stress and antioxidant enzyme activity in erythrocytes. Twenty male volunteers were randomly assigned to 2 groups: PRT and control. Blood samples were collected before and after 8 wk of PRT and analyzed for enzymatic activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) in erythrocytes, plasma total antioxidant capacity (TAC), and malondialdehyde concentration (MDA, an index of lipid per oxidation in plasma). Resistance training commenced with 8 exercises on nonconsecutive days for 8 wk at 50% of estimated 1-repetition maximum (E1RM) and reached 80% E1RM by Week 8. The results showed that PRT significantly increased erythrocyte SOD activity (1,323 ± 212.52 vs. 1,449.9 ± 173.8 U/g Hb, p = .014). Plasma concentration of MDA also decreased (5.39 ± 1.7 vs. 3.67.4 ± 0.7 nmol/ml, p = .030), although TAC (1.42 ± 0.21 vs. 1.61 ± 0.19 mmol/L, p = .1530) and GPx (39.87 ± 11.5 vs. 48.18 ± 14.48 U/g Hb, p = .883) activity did not undergo any considerable changes. Based on these data, the authors conclude that an 8-wk program of PRT strengthens the defensive system of erythrocytes against free-radical damage and therefore can be applied as a useful approach to alleviate oxidative stress.