Aim To study the effect of proteasome inhibitor MG132 on the expression of caspase-3 and apoptosis in cultured human umbilical vein endothelial cells.Methods Human umbilical vein endothelial cells was treated with MG132 (2,5 μmol·L~(-1)) for 24 h. The apoptotic cells were determined by DNA fragment analysis and flow cytometric analysis. The level of caspase-3 mRNA was quantified by reverse transcription-polymerase chain reaction (RT-PCR). The protein contents of caspase-3 were analyzed by immunocytochemistry.Results The results showed that the increase of the degree of human umbilical vein endothelial cells apoptosis was concentration dependent. MG132 could up-regulate the gene/protein expression of caspase-3.Conclusions The results implicated that proteasome inhibitor MG132 induced human umbilical vein endothelial cells apoptosis by accumulation of caspase-3.