Lipopolysaccharide (LPS) from Gram-negative bacterial has been identified as an important molecule involved in the inflammatory process through inducing nitric oxide (NO) production. However, the effect of LPS in carcinogenesis is still undefined. In the present study, the biological effect of LPS was examined in 12-o-tetradecanoylphorbol 13-acetate (TPA)-treated rat glioma cells C6. Results of MTT assay showed that LPS and TPA exhibited no significant cytotoxicity in glioma C6 cells. Interestingly, transformation foci were found in LPS/TPA-treated glioma C6 cells, but not in LPS- or TPA-treated cells. The transformation foci induced by LPS/TPA were also observed in the absence of serum. It indicates that induction of transformation foci formation by LPS and TPA is independent on the serum in glioma C6 cells. Induction of iNOS gene expression and NO production was examined in LPS/TPA-treated cells, but not obvious in LPS- or TPA-treated cells. NO donor sodium nitroprusside (SNP) induces transformation in glioma C6 cells in according with elevating NO production. In addition, LPS/TPA induces metalloproteinase 9 (MMP9) activity by gelatin activity assay in gel. Wogonin and quercetin but not rutin, inhibitors of iNOS gene expression and NO production induced by LPS, showed the significant inhibition on LPS/TPA-induced transformation foci formation, accompanied by inhibiting iNOS gene expression, NO production and MMP9 activity. Results of the present study provide scientific evidences to link the inflammatory responses and carcinogenesis, and suggest that NO derived from inflammation may contribute to the progression of carcinogenesis; natural products with anti-inflammatory effects such as wogonin and quercetin possess the ability to block transformation induced by LPS/TPA.