This study was performed to assess age-related changes in DNA damage and antioxidative capacity in 4, 8, 12, 16, 20, and 24 months old Sprague-Dawley male rats. The following were measured the degree of oxidative DNA damage as indicated by levels of 8-hydroxy-2′-deoxyguanosine (80HdG) in the kidney ; the peroxidized lipid concentrations in the plasma and the liver, as indicated by the levels of thiobarbituric acid reactive substances (TBARS); and the levels of antioxidant enzyme activities in the erythrocytes and the liver. Both body weight (BW) and epididymal fat pad (EFP) weight per BW increased with age until 16 months, then decreased slightly from 20 to 24 months. However, the weights of the liver, kidney and spleen per BW decreased with age. Concentrations of 8-OHdG in the kidney increased with age, only slightly front 4 to 16 months, and then markedly from 16 to 24 months. TBARS concentrations in the plasma and liver were shown to increase with age, being lowest in the 4 month-old group and highest in the 24 month-old group. Superoxide dismutase (SOD) activity in the erythrocytes increased with age Catalase activity in the erythrocytes increased from 4 to 16 months, then decreased from 20 to 24 months. Glutathione peroxidase (GSH-Px) activity in the erythrocytes showed no age-related change. Liver SOD activity decreased with age, particularly from 16 to 20 months, but catalase and GSH-Px activities in the liver showed no significant changes. These results showed that during the normal aging of SD rats, DNA damage in the kidney and TBARS concentrations in the plasma and liver increased with age, particularly after 16 months, and the imbalance of antioxidative enzyme activities in the erythrocytes accelerated with age.