Vascular endothelial growth factor (VEGF) has been implicated in breast tumor angiogenesis. And tumor necrosis factor-α (TNF-α) is a positive regulator of VEGF. This study was aimed to identify the signalling pathway of TNF-α in VEGF expression regulation in breast cancer cell line MCF7. Using luciferase reporter assays, we demonstrated that TNF-α significantly increased activator protein-1 (AP-1) transcriptional activity in the MCF7 cells. The expression of the AP-1 family members c-Jun, c-Fos and JunB and phosphorylation levels of c-Jun were upregulated by TNF-α, whereas other AP-1 family members Fra-1, Fra-2, and JunD were unaffected. The activation of AP-1 was associated with the formation of p-c-Jun-c-Jun and p-c-Jun-JunB homodimers. Furthermore, the phosphorylation levels of c-Jun N-terminal kinase (JNK) but not P38 and ERK were elevated by TNF-α in MCF7 cells. TNF-α potently upregulated the mRNA and protein levels of VEGF, which were significantly reversed by JNK inhibitor SP600125. Finally using chromatin immunoprecipitation (CHIP) assays, we found that p-c-Jun bound to the VEGF promoter and regulated VEGF transcription directly. These data suggest that the pro-inflammatory cytokine TNF-α is a critical regulator of VEGF expression in breast cancer cells, at least partially via a JNK and AP-1 dependent pathway.