Aim To investigate the effects of cobra cardiotoxin-13 (CTX-13) on the apoptosis of human umbilical vein endothelial cells (HUVEC) and the expression of Bcl-2 family.Methods The effect of CTX-13 on HUVEC proliferation was analyzed by CCK-8 assay.The morphological changes were observed with Annexin V-FITC/PI staining.The DNA ploidy analysis and apoptotic rates assay were performed by flow cytometry.The expression level of Bcl-2 gene family was measured by RT-PCR and Western blotting.Results CTX-13 caused a dose-dependent decrease of cell viability and displayed several features of apoptosis including translocation of membrane phosphatidylserine and increase of sub G1 hypodiploid cell population.The apoptotic rates of HUVEC treated with CTX-13 concentrations of 0.3,0.75,1.5 μmol/L were 20.50%±2.62%,54.20%±4.93% and 93.40%±6.45%.CTX-13 up-regulated the mRNA expression of Bax about 4-fold as well as its protein expression,but did not affect the expression of Bcl-2 and Bcl-xL.Conclusions CTX-13 suppressed HUVEC proliferation significantly and induced apoptosis in a dose-dependent manner.CTX-13 up-regulated Bax in mRNA and protein level.It was probable the CTX-13 suppressed proliferation and induced apoptosis by up-regulating Bax.