This study was conducted to investigate the effect of acorn extracts on the antioxidative enzyme system. Male Sprague-Dawley rats(110$pm$10g) were fed on containing normal and high fat diets. They were orally administrated (0.02g/100g B.W) of acorn ethylacetate-extract and water-extract at the same time once a day, respectively. Net weight gain and feed efficiency ratio were increased in high fat diet groups and decreased by acorn extracts administration. The effect of acorn extracts on hepatic glutathione peroxidase(GSH-Px), glutathione S-transferase(GST) and catalase activities did not show significancy in normal fat diet groups. GST and catalase activities and lipid peroxidation content(LPO) were significantly increased in high fat diet groups and this increment were decreased by acorn extracts administration. However GSH-Px activity and GSH content were decreased in high fat diet groups but increased by acorn extracts administration. The activities of lactate dehydrogenase(LDH), alkaline phosphatase(ALP) and aminotransferase in serum were significantly increased in high fat diet group but these increment reduced in acorn extracts administration groups. These results indicate that acorn extracts could improve the liver function and prevent the metabolic diseases by hyperlipidemia.