Objective: MiR-16 plays a critical role as a tumor suppressor by targeting several oncogenes such as genes controlled cell cycle and apoptosis. Hence, miR-16 could act as an important anti-tumor agent in most cancers. In the present study, we investigated the functional role of miR-16 on breast cancer growth and survival. Materials and Methods: Human breast cancer cell line, MCF-7, was infected with lentiviruses containing miR-16 precursor sequence. The effects of ectopic expression of miR-16 on breast cancer phenotype were examined by cell cycle and apoptotic assays. miR-16 cytotoxicity was measured by the MTT assay. Results: We showed that the miR-16 over expression reduces CyclinD1 mRNA and Bcl2 protein levels. In addition, we found that enforced expression of miR-16 declined cell growth, proliferation and induces apoptosis. Conclusion: Taken together, our results revealed that the up-regulation of miR-16 would be a potential approach for breast cancer therapy that induces G1 arrest and apoptosis.