Matrix metalloproteinases (MMPs) play an important role in cancer metastasis, cell migration and invasion. Herein, we investigated the effects of silibinin on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced cell migration and MMP-9 expression in thyroid and breast cancer cells. Our results revealed that the levels of MMP-9 mRNA and protein expression were significantly increased by TPA but not MMP-2 in TPC-1 and MCF7 cells. To verify the regulatory mechanism of TPA-induced MMP-9 expression, we treated TPC-1 and MCF7 cells with the MEK1/2 inhibitor, UO126, and TPA-induced MMP-9 expression was significantly decreased. We also found that TPA-induced cell migration and MMP-9 expression was significantly decreased by silibinin. In addition, TPA-induced phosphorylation of MEK and ERK was also inhibited by silibinin. Taken together, we suggest that silibinin suppresses TPA-induced cell migration and MMP-9 expression through the MEK/ERK-dependent pathway in thyroid and breast cancer cells.