To evalulate the antioxidant effect of flavonoid(+)-catechin on n-3 polyunsaturated fatty acids in vivo, rats were fed with diets containing $5\%$ corn oil(CO), $5\%$ corn oil and $15\%$ purified fresh fish oil(FO) or peroxidized fish oil(PFO) for 10 days. To accerelate lipid peroxidation, all of them were injected with 60mg phenobarbital(a day per kg body weight), and treated with phorone(diisopropylidene acetone) before the rats were killed. Contents of triglyceride, phospholipid, cholesterol and lipid peroxide and the activities of GOT, GPT in serum and total lipid and cholesterol content in liver of PFO group rats were significantly higher than those of the FO one. Contrary to our expectations, the activities of superoxide dismutase (SOD), catalase and glutathione peroxidase(GSH-Px) in liver of the FO group were ]ewer than those of the PFO group. These results might be explained as the results of homeostasis. Even though the hepatic glutathione were depleted, catechin and a-tocopherol inhibited production of lipid peroxide effectively. These results suggested that catechin be considered an antioxidative and hepatoprotective agent.