Aim To investigate the effects of hydrogen sulfide on ox-LDL-induced apoptosis in human umbilical vein endothelial cells(HUVEC) and the mechanisms involved.Methods The HUVEC were incubated with ox-LDL for 24 hours after treatment with NaHS at different concentrations(25,50,100,200 μmol/L) for 24 hours or for different incubation time(6,12,24 hours) at the concentration of 50 μmol/L.The apoptotic alterations of HUVEC were observed by Hoechst 33258 staining and flow cytometry(FCM),respectively.The change of mitochondrial membrane potential(MMP) and intracellular reactive oxygen species(ROS) generation were detected by Dihydrohodamine123(DHR123) staining and rhodamine123(Rh123) staining.Results Pre-treatment with NaHS remarkably inhibited apoptosis induced by ox-LDL in HUVEC in a time-and concentration-dependent manner(all P<0.01).The decrease of MMP and increase of the intracellular ROS generation in HUVEC induced by ox-LDL were significantly prohibited by treatment with NaHS or N-acetyl-L-cysteine(NAC)(all P<0.05).Conclusions H2S inhibits apoptosis induced by ox-LDL in HUVEC which is involved in preservation of mitochondrial membrane potential and attenuation of the intracellular ROS generation.