Objective To investigate the influence of Ulinastatin (UTI) on the hyper-permeability of vascular endothelial cells induced by tumor necrosis factor alpha (TNF-α).Methods Inflammation model was induced by TNF-α in human umbilical vein endothelial cell line (EA.hy926).The experiment was designed into 4 groups:normal group,TNF-α group,UTI group and TNF-α with UTI (U + T) group.Methyl thiazolyl tetrazolium (MTT) method and epithelial voltameter (EVOM) method were used to measure cell viability [absorbance (A) value] and transepithelial electrical resistance (TER) of EA.hy926 cells respectively.The expression of VE-cadherin was measured by reverse transcription polymerase chain reaction (RT-PCR) and immunocytochemistry.Results Compared with normal group,the TER of EA.hy926 cells induced by TNF-α was significantly decreased (67.200 ± 8.937 vs.33.600 ± 8.771,P =0.010).The permeability in EA.hy926 cells increased obviously.The hyper-permeability of EA.hy926 cells induced by TNF-α could be alleviated by UTI at the concentrations of 1-100 U/mL in a dose-dependent manner (40.133 ±7.484 vs.33.600 ±8.771,P=0.382;49.232 ± 3.162 vs.33.600 ± 8.771,P =0.044;63.700 ± 8.515 vs.33.600 ± 8.771,P =0.013).The expression of VE-cadherin mRNA reduced significantly in the TNF-α group (1.089 ±0.018 vs.0.835±0.021,P =0.000) compared with normal group.This effect of TNF-α could be attenuated by UTI.When EA.hy926 cells exposed to UTI at 10 U/mL and 100 U/mL,a significant increase of the expression of VE-cadherin mRNA was observed (0.976 ±0.014 vs.0.835 ±0.021,P =0.001;1.115 ±0.015 vs.0.835 ± 0.021,P =0.000).And the inhibition of UTI manifested a dose-dependent manner (1-100 U/mL).The results of the immunocytochemistry showed that the expression of VE-cadherin in TNF-o group was decreased significantly (0.061 ± 0.013 vs.0.093 ± 0.014,P =0.049) compared with normal group.And the low-expression of VE-cadherin could be alleviated by UTI (0.032 ± 0.004 vs.0.061 ± 0.013,P =0.016).Conclusion The high permeability of EA.hy926 cells induced by TNF-α could be inhibited by UTI at the concentrations of 1-100 U/mL in a dose-dependent manner.