The health-promoting effects of antioxidant vitamins C and E supplementation are unclear. This study investigated the effects of vitamins C and E on the activities of reactive oxygen species (ROS)-scavenging enzymes and protein and lipid peroxidation statuses under resting and exercise-induced conditions. Thirteen healthy, previously untrained males (age 20–21 years) participated in this study. Seven subjects performed physical exercise using a cycle ergometer, and six performed a 6-min walk test (6MWT) prior to vitamin administration and after 1-week oral administration of vitamin C (1000 mg/day) and vitamin E (300 IU/day). Venous blood samples were collected before and after exercise. Plasma vitamin C concentration, superoxide dismutase (SOD) activity, glutathione peroxidase (GPx) activity, and protein carbonyl and thiobarbituric acid-reactive substance (TBARS) contents were measured. Antioxidant supplementation increased vitamin C concentration by 34% (p<0.05), decreased SOD activity by 17% (p<0.05), increased GPx activity by 13% (p<0.05), and increased the GPx/SOD activity ratio by 37% (p<0.05). Protein carbonyl and TBARS contents were unaffected. Antioxidant vitamins effectively increase the plasma GPx/SOD activity ratio, but fail to reduce protein carbonyl levels induced by exercise.