Atherosclerosis is caused by deposits of lipids in the arteries. Lipids containing oxidized unsaturated fatty acids and protein form complexes which have strong linkages unable to be separated by solvent extraction. If oxidized lipids form the complexes with protein of arterial wall, deposits of cholesterol and its esters of fatty acids may occur around the complexes. In this case oxidized lipids may be detected in the lipids of arteries. From this point of view, lipids were extracted from atherosclerotic artery with methanol-chloroform (1 : 2) at room temperature. Fatty acids, and then methyl esters were obtained from the lipids. All procedures were performed at room temperature under the atmosphere of nitrogen. Fatty acids composition was calculated from the results of ultra-violet spectrum analysis. It became clear that trans-trans conjugated diene hydroperoxide exists in the methyl ester from the infra-red spectrum. No hydroperoxides were found in the lipids of normal artery.