Vanillin has been reported to exhibit anti-invasive and antimetastatic activities by suppressing the enzymatic activity of matrix metalloproteinase-9 (MMP-9). However, the underlying mechanism of anti-invasive activity remains unclear so far. Herein we demonstrate that vanillin reduced 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced MMP-9 gelatinolytic activity and suppressed cell invasion through the down-regulation of MMP-9 gene transcription in HepG2 cells. Vanillin significantly reduced the 6.6-fold invasive capacity of HepG2 cells in noncytotoxic concentrations, and this anti-invasive effect was concentration-dependent in the Matrigel invasion assay. Moreover, vanillin significantly suppressed the TPA-induced enzymatic activity of MMP-9 and decreased the induced mRNA level of MMP-9. Analysis of the transcriptional regulation indicated that vanillin suppressed MMP-9 transcription by inhibiting nuclear factor-kappaB (NF-kappaB) activity. Western blot further confirmed that vanillin inhibited NF-kappaB activity through the inhibition of IkappaB-alpha phosphorylation and degradation. In conclusion, vanillin might be a potent antiinvasive agent that suppresses the MMP-9 enzymatic activity via NF-kappaB signaling pathway.