Background: Mir-181a has been considered as an attractive molecular target for breast cancer therapy. The main objective of this work is to assess the inhibitory effects of silibinin, a herbal substance, on proliferation, apoptosis and Mir-181a gene expression in human breast cancer cell line SK-BR-3. Materials and Methods: Human breast cancer cell line SK-BR-3 was treated with various concentration of silibinin. Cell viability was assessed by MTT assay and apoptosis by flow cytometry. Expression of human mir-181a gene was measured with real-time PCR. Results: Silibinin inhibits growth of SK-BR-3 cells in a dose-and time-dependent manner and effectively induces apoptosis of SK-BR-3 cells. In addition, silibinin caused a decrease in Mir-181a level. Conclusion: These findings suggest that cell viability along with Mir-181a gene expression in breast cancer cells could be reduced by silibinin. These results suggest that silibinin inhibits the proliferation of SK-BR-3 cells, and it induces apoptosis by down-regulating Mir-181a expression in breast cancer cells.