Physical activity is associated with beneficial changes in serum lipids, but exhaustive exercise has been suggested to increase oxidative stress. To test the effect of ascorbate (vitamin C) on serum lipids and the metabolism of urate, which is the most important intrinsic antioxidant, during exhaustive exercise, we performed a randomized, blinded, placebo-controlled study on eight male well-trained athletes. Subjects were randomly allocated to either a group given 1000 mg of ascorbate daily (n=4) or a placebo group (n=4). Fasting serum lipids and urate concentrations were measured before and after 3 weeks of training. Although serum low-density lipoprotein (LDL)-cholesterol levels decreased and high-density lipoprotein (HDL)-cholesterol levels increased significantly in the ascorbate group after the 3 weeks of training, serum LDL-cholesterol levels increased and HDL-cholesterol levels decreased significantly in the placebo group. Furthermore, serum urate levels were elevated significantly in the placebo group; however, these levels did not change in the ascorbate group. When compared with the placebo group, significantly higher serum HDL-cholesterol and lower serum LDL-cholesterol and urate levels were observed in the ascorbate group after training. In conclusion, our results suggested that ascorbate may contribute to the desirable changes in serum lipids during exhaustive training and suggest the significant association between ascorbate and urate under intense training.