Rubi Fructus (fruit of Rubus coreanus Miq.), oriental medicine, has been used for remedy of the liver diseases and for tonic. In order to investigate the oxygen free radical, a harmful factor of aging, in liver of rats fed diets supplemented with the Rubi Fructus water extract(RX), Sprague-Dawley male rats have been fed a diet supplemented with 3% or 5% RX for a month. In rats fed 3% RX supplemented diet, hepatic cytochrome P-450 contents appeared to be increased, and catalase and superoxide dismutase activities were significantly increased compared with the control. There was no difference in glutathione peroxide and glutathione-S-transferase activities between the rats fed RX supplemented diets and the control diet. In conclusion, it is likely that rats fed a diet supplemented with RX may have the oxygen free radicals detoxication potential.