AIM:To evaluated weather homocysteine(Hcy) and low density lipoprotein(LDL) had co-effects in pathogenesis of atherosclerosis (As). METHOD: Thiobarbituric acid reactive substance (TBARS) and apoptotic cells were measured after endothelial cell(EC) being exposed commonly or separated to Hcy and LDL. RESULTS: TBARS content in Hcy +LDL group was 4.9～7.7 times of that in single Hcy or LDL group, even put together TBARS contents of single Hcy or LDL groups, the co-effect of Hcy+LDL still showed 3 times higher than the former. Furthermore, Hcy+LDL showed obvious apoptosization effect on EC. The lipid peroxidization and EC apoptosization effects of Hcy+LDL were inhibited by adding folic acid , L-arginine+folic acid or glutamate+glycine. CONCLUSION: Hcy+LDL have co-injury effects on EC which may lead to As. The pathogenic factors of these effects probably involve the thiol groups of Hcy and their injury on nitric oxide system of EC.ESULTS :TBARScontentinHcy +LDLgro