Objective:To investigate the effect of CDAII on apoptosis of breast cancer cells. Methods:The effects of CDAII on growth curve, cell apoptosis and morphology of breast carcinoma cell lines MCF7 and MDAMB231 were observed by in vitro cultures, and compared with the classical cell differentiation inducer ATRA. MCF7 and MDAMB231 cell lines have their different biologic characteristics. Results:CDAII can reduce growth and proliferation ability and induce cell apoptosis of breast cancer cell lines( MCF7 and MDAMB231). Conclusions:CDAII has remarkable effect of anticellproliferation and induction of apoptosis on breast cancer cells MCF7 and MDAMB231 . Our results provide experimental bases for the treatment of breast carcinoma with CDAII.