Abstract: Objective: To study the occurence of apoptosis and the related mechanism of the human umbilical vein endothelial cells (HUVEC) induced by Ureaplasma urealyticum (UU).Methods: The occurence of apoptosis of HUVEC was determined by flow cytometry at different times (2,4,8 and 12 h) after infected by UU.The productions of TNF-α,caspase-3 and caspase-8 in HUVEC after 8-hour infection of UU were detected by colorimetric assay,and the apoptosis rates were determined by flow cytometry when HUVEC was treated with TNF-α antibody,caspase-3 inhibitor or caspase-8 inhibitor prior to UU.Results: UU could induce the apoptosis occurrence of HUVEC with significant difference compared with control group.The productions of TNF-α,caspase-3 and caspase-8 were increased significantly in HUVEC infected by UU in contrast to control group,and the apoptosis occurence was significantly decreased when HUVEC was treated with TNF-α antibody,caspase-3 inhibitor or caspase-8 inhibitor.Conclusions: The results suggested UU could induce the apoptosis occurrence of HUVEC with time-dependence.The mechanism was likely related to extrinsic death pathway dependent on TNF death receptor which induced caspase-8 and caspase-3 activations.