Abstract: Objective: To investigate the effect of CDA-II on the cell apoptosis and bcl-2 expression of breast cancer cells. Methods: The effect of CDA-II on cell growth, cell apoptosis, the expression of bcl-2 and morphology of breast carcinoma cell lines MCF-7 and MDA-MB-231 were observed in vitro cultures, in comparison with the classical cell differentiation inducer ATRA. MCF-7 and MDA-MB-231 have their different biologic characteristics. Results: CDA-II could reduce the growth speed, proliferation ability and bcl-2 expression and induce apoptosis of breast cancer cell lines. Conclusion: CDA-II has remarkable effect on anti-cell-proliferation, decrease expression of bcl-2 and induce apoptosis of breast cancer cells. Our results provide experimental proves for the treatment of breast carcinoma with CDA-II.