The present invention relates to a prophylactic/therapeutic agent for atherosclerosis comprising GM3 synthase inhibitor or inhibitor for expression of GM3 synthase gene, a diagnostic product for atherosclerosis comprising antibody to GM3 synthase, a method of diagnosis for atherosclerosis using antibody to GM3 synthase and others, an use of GM3 or GM3 synthase for diagnostic marker of atherosclerosis, and the like.