Summary: To observe the effect of oxidized low density lipoprotein (OxLDL) on arterial endothelialcells apoptosis in vivo, we established a model in which Sprague-Dawley rats were given intraperi-toneal and intravenous injection of unmodified LDL (8 mg/kg every day) via the tail vein. Sevendays after the injection, the aortic endothelial cells specimens were prepared by an en face preparationof rat aorta. The apoptotic cells were identified and counted by in situ nick and labelling (TUNEL)method and light microcopy. The numbers of the apoptotic cells were 12.52±4.71/field in the in-traperitoneal injection control group, 11.41±2.94/field in the intravenous injection control group,22.98±8. 01/field in the intraperitoneal injection LDL group and 103. 8 ± 11.5/field in the intra-venous injection LDL group, respectively. The difference was significant between injection LDLgroup and control (P＜0. 01), and the difference was also significant between two LDL injectiongroups (P＜0. 01). These findings suggest that injection of LDL can induce apoptosis in arterial en-dothelial cells and the effect is especially significant with intravenous injection LDL. After injection,oxidative modification of LDL may occur in local arteries and causes injury to the endothelial cells.