This study was intended to investigate the effects of regular swimming exercise and vitamin C supplementation on the antioxidant system following exercise stress. For the swimming exercise experiment, a swimming adaptation exercise of 1 week was given to a group of 6-week-old mice. Following this, a swimming exercise for 8 weeks was conducted. The experimental group was divided into 3: a control group (C), a swimming exercise trained group (T), and a group of swimming + vitamin C supplementation (TC: vitamin supplementation: 1.3 mg/l00 g diet). After the swimming exercise, these group were further divided into those that had received the exercise stress for 2 hours and those that had not experienced exercise stress group. Then, the activities of the superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and malondialdehyde (MDA) concentrations were measured. There was a lower weight increase in the T and TC groups than in the C group, and there was no significant difference between T and TC group. When exercise stress was not experienced, the activity of SOD was significantly increased in the TC group than in the T group, but there was no significant difference between C and T groups. The groups that had experienced a 2-hour exercise stress showed the SOD activity levels according to the following order, C < T < TC, with a significant difference between the three groups (p<0.05). There was no difference in MDA concentration amongst the experimental groups in non-exercise stress group. As well, there was no differences in MDA concentration between the C group and T group in the 2 hour exercise stress group. However, the TC group showed a MDA concentration level significantly lower than that of the T group. A significant increase in MDA concentration was observed in C group, when exercise stress was provided with no significant difference in the T and TC groups. As a result, regular exercise and vitamin C supplementation can be considered important in controlling the formation of lipid peroxides in exercise stress.