Objective:To study the protective effects and mechanisms of oleanic acid on damaged human umbilical vein endothelial cells (HUVECs) induced by hydrogen peroxide (H2O2). Methods:HUVECs were divided into control group,H2O2 group(200 mol/L H2O2 treatment),H2O2 of 200 mol/L combined with OA of 0.25 mol/L treatment group,H2O2 of 200 mol/L combined with OA of 0.50 mol/L treatment group,H2O2 of 200 mol/L combined with OA of 1.00 mol/L treatment group,H2O2 of 200 mol/L combined with vitamin C of 1.50 mmol/L treatment group. Cell viability was determined by MTT method. Lactate dehydrogenase(LDH) and nitric oxide (NO) content in the supernatant were determined by biochemical method. The activity of malondialdehyde(MDA),glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD) in the cell lysate was determined by biochemical method. Intracellular reactive oxygen species (ROS) and cell apoptosis were determined by flow cytometry. Results:OA restored the H2O2-injuried cell viability,reduced the H2O2-induced LDH release,and reduced H2O2-induced MDA formation,recovered H2O2-injuried GSH-Px and SOD activity,removed H2O2-induced ROS,reduced the H2O2-induced apoptosis,and enhanced the NO production in HUVECs. Conclusion:OA has a protective effect on HUVECs,which is related to initiating the antioxidant defense,getting rid of ROS,inhibiting H2O2-induced apoptosis,and improving NO production in HUVECs.