Abstract: Objective 　To study thrombin for the up-regulation of vascular endothelial growth factor on the human non-small cell lung cancer cells line A549, and to explore it s mechanism. Methods 　The ELISA methods was used to evaluate the role of thrombin on the expression of vascular endothelial growth factor (VEGF) in A549 and inhibition of hirudin. RT-PCR was used to evaluate the expression of thrombin receptor (PAR-1) in A549 cell. Results 　Thrombin may increase the secretion of VEGF in A549 cell in 0. 5～3 U/ ml concent rations. The induction of VEGF was significantly blocked by the thrombin inhibitor hirudin. RT-PCT demonst rated PAR-1 expressed in A549 cell but not in KMB-17. Conclusion 　Thrombin may substantially stimulate the secretion of VEGF in A549 cell within a certain degree. The mechanisms of induction were might related with the expression of thrombin receptor PAR-1.