The effects of isorhamnetin, rhamnetin and quercetin on the serum and liver cholesterol concentrations, liver lipoperoxide (thiobarbituric acid-reactive substances: TBARS) content, and antioxidative enzyme activities were examined with rats fed on cholesterol-enriched and cholesterol-free diets. The total serum cholesterol of those rats fed with the cholesterol-enriched diet was decreased by feeding each all these flavonoids. The total liver cholesterol concentration and TBARS content in the rats fed with the cholesterol-free diet were decreased by feeding isorhamnetin, rhamnetin and quercetin. The activities of liver superoxide dismutase and catalase were almost unaffected by feeding these flavonoids. These results, the in vitro antioxidative activities of isorhamnetin, rhamnetin and quercetin, and the activities of these flavonoids in suppressing the generation of the superoxide anion in vitro suggest the possibility that the lower liver TBARS content in those rats fed on the cholesterol-free diet with added flavonoids is ascribable in part to the direct antioxidative and superoxide anion generation-suppressing activities of flavonoids and/or their metabolites absorbed from the gastrointestinal tract.