Abstract: Objective: To investigate the effect of CDA-II on the expression of bcl-2 of breast cancer cells. Methods: The effect of CDA-II on growth curve, 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: The growth speed, proliferation ability and bcl-2 expression of breast cancer cell lines can be reduced by CDA-II. Conclusion: CDA-II has remarkable effect on anti-cell proliferation and can decrease expression of bcl-2 on breast cancer cells. Our results provide the experimental bases for the treatment of breast carcinoma with CDA-II and also suggest that CDA-II show good prospects of application for the treatment of breast carcinoma.