Aim The pathological mechanism of high occurrence of atherosclerosis in diabetes mellitus (DM) has not been clear. The purpose of this study is to detail its possible mechanism by studying whether high glucose and LDL could synergetically injure vascular endothelial cells (ECV304). Methods Glucose (5.5, 20 and 40 mmol/L) and/or LDL (100 mg/L) was added into the medium of cultured endothelial cells and incubated for 24, 48, and 72 h respectively. The lipid peroxidation was assessed by the content of TBARS, apoptosis and cell cycle were studied with Giemsa staining, transmission electron microscopy and Coulterepics SP. Results (1)High glucose could enhance cell mediated LDL peroxidation and showed a position of dose effect relationship. (2)High glucose and LDL had synergetical effects on inducing apoptosis. This may be preferentially related to the cell mediated LDL peroxidation enhanced by high glucose and prolongation cell cycle traversal of endothelial cells through oxidative stress produced by high glucose. Conclusion High glucose and LDL could synergetically induce apoptosis in endothelial cells, which aggravate the pathogenesis of atherosclerosis in diabetes mellitus. This may at least partly attribute to the mechanism that diabetes mellitus mostly accompany high risk of atherosclerosis.