Aim To study the influence of tumor necrosis factor α (TNF α) on plasminogen activator inhibitor 1 (PAI 1) activity, gene expression and regulation in human umbilical vein endothelial cell (hUVEC). Methods The PAI 1 activity in hUVEC culture medium was measured by chromogenic assay. The PAI 1 mRNA expression were determined by Northern blot. Using gene recombination techniques, four luciferase reporter gene plasmids containing different length of human PAI 1 gene promoter were constructed. Through the transient transfection analysis, the roles of AP 1 element (from -823 bp to -553 bp) in PAI 1 promoter have been determined. In order to further verify the role of AP 1 element, the three site directed mutants were received using polymerase chain reaction (PCR) and sequencing assay. Results The PAI 1 activity and mRNA level increased when hUVEC were exposed to 100 ku/L TNF α. At the same time, the AP 1 protein level increased in nuclear. The induction by TNF α decreased markedly when the three AP 1 elements in PAI 1 promoter have been mutated respectively. Conclusions TNF α could induce PAI 1 activity and mRNA in hUVEC; Increase of PAI 1 activity induced by TNF α was related to its mRNA expression; Three AP 1 elements in PAI 1 promoter may have an important role in PAI 1 gene transcriptions in endothelial cells induced by TNF α.