Abstract: AIM To observe the effect of tumor necrosis factor-α( TNF-α) on the expression and activity of thrombomodulin( TM) in human umbilical vein endothelial cells( HUVECs) and to investigate its mechanism. METHODS HUVECs were incubated in vitro and the experiment was conducted using three groups: control group,TNF-α group( incubated with TNF-α 10 ng / ml for 6 h) and BAY11-7082 suppression group first incubated with BAY11-7082 2 μg / ml for 1h,then incubated with TNF-α( 10 ng/ml) for 6 h. Flow cytometric and RT-PCR technique were used to detect TM protein and mRNA,and Microplate Reader was used to detect TM activity. RESULTS Compared with those in the control group and BAY11-7082 suppression group,both mRNA and protein levels of TM were significantly reduced( P < 0. 05) and the TM activity in HUVECs was inhibited( P < 0. 05) in TNF-α group. However,compared with those in the control group,no statistical differences were observed in the protein level of TM and the TM activity,whereas mRNA levels of TM were increased( P < 0. 05) in the BAY11-7082 suppression group. CONCLUSION Exposure to TNF-α significantly decreases the expression of TM and inhibits the TM activity in HUVECs. NF-κB pathway plays a role in this process.