Abstract. Morusin which has been isolated from the root bark of Morus alba L. (Moraceae) has previously demonstrated anticancer activity in various types of cancer cells such as hepatocellular carcinoma, glioma and prostate cancer. However, the effect of morusin on breast cancer cells remains unclear. In the present study, the potential of morusin as an anti-cancer agent in breast cancer was investigated. The results of the present study revealed that the treatment of morusin induced cell death in various human breast cancer cell lines, but exhibited little effect on normal human breast epithelial cells. In Annexin V-propidium iodide double staining assays, morusin significantly increased apoptosis in a dose-dependent manner in human breast cancer cells. The apoptosis marker proteins cleaved caspase 3 and 9 were consistently upregulated following treatment of cells with morusin in a time-and dose-dependent manner. Furthermore, morusin was demonstrated to modulate the expression of the anti-apoptotic protein Survivin and pro-apoptotic protein B-cell lymphoma 2-associated-x protein (Bax) in human breast cancer cells. These results indicate that morusin induces apoptosis by suppressing Survivin and inducing Bax proteins, suggesting that morusin is a potentially effective therapeutic agent for the treatment of patients with breast cancer.