Objective To explore the role of the transcriptional factor activator protein (AP)-1 in mediating vascular endothelial growth factor ( VEGF) expression in human bronchial epithelial cells exposed to PM 2.5.Methods Beas-2B cells was treated with PM2.5.Luciferase assay was used to detect the activation status of AP-1 and transcription of VEGF in the Beas-2B cells.The induced activation of c-Jun, ATF2 and VEGF expression was tested by Western blotting assay.Results PM2.5 induced transactivation of the transcriptional factor AP-1, accompanied by phosphorylation of the AP-1 components, c-Jun and ATF2 in Beas-2B cells.Moreover, when AP-1 activation was inhibited by knocking down c-Jun or ATF2 expressions, induction of VEGF expression was partially attenuated in Beas-2B cells.Conclusion AP-1 is a critical transcriptional factor in mediating PM2.5-induced VEGF expression and inflammatory responses in human bronchial epithelial cells.