We investigated the effects of the water extracts of the fruiting bodies of cultured Cordyceps sinensis (WECS) on lipid metabolism in mice fed an atherogenic diet. WECS was orally administered at doses of 50, 100 and 200 mg/kg/day for 12 weeks. WECS showed no toxic effects on the growth rate, liver or kidney weights of the mice. Mice fed the atherogenic diet showed marked increases in serum lipid and lipid peroxide levels and also aortic cholesterol levels, particularly cholesteryl ester level, a major lipid constituent in atherosclerotic lesions. WECS significantly suppressed the increased serum lipid peroxide level but not other lipid levels in a dose-dependent manner. WECS also suppressed the increased aortic cholesteryl ester level in a dose-dependent manner. These results suggest that WECS prevents cholesterol deposition in the aorta by inhibition of LDL oxidation mediated by free radicals rather than by reduction in serum lipid level. WECS may exert beneficial effects on the formation of the atherosclerotic lesion induced by oxidative stress with few side effects.