Aim To study the protective effect of onychin against vascular endothelial cell apoptosis induced by oxida tive stress. Methods Cultured human umbilical vein endothelial cells (ECV304) were incubated for 30 min with either vehicle (DMSO), genistein or onychin before being challenged with H₂O₂ . Cell viability were measured by the MTT assay, and cell apoptosis was determined by flow cytometric analysis and terminal deoxynucleotidyl transfersas-mediated dUTP nick end-labeling (Tunel) respectively. Meanwhile, Western blot was used to measure the activation of caspase-3. Results H₂O₂ treatment for 24 h evoked endolhelium apoptosis, and onychin (0.3, 1 and 3 μmol/L.) decreased the rate of apoptoic endothelial cells (15. 5%±1.2%, 12.6% ±0.9% and 8.2% ±0.8% vs 22.7% ± 3.9% )in a concentration-dependent manner. Meanwhile, Onychin decreased the expression of active caspase-3 induced by H₂O₂ as genistein. Conclusion onychin prevents H₂O₂-in-duced endothelium apoptosis which correlated with inhibition of caspase-3 activation.