【Abstract】ObjectiveTo investigate the effect of CDAⅡ on the cell cycle progression of breast cancer cells.MethodsThe effects of CDAⅡ on growth curve, cell cycle progression and morphology of breast cancer cell lines MCF7 and MDAMB231 were observed when CDAⅡ and MCF7 or CDAⅡ and MDAMB231 were blended to cultivate in vitro, in comparison with the classical cell differentiation inducer ATRA. ResultsCDAⅡ decreased the growth speed and inhibit proliferation ability in breast cancer cell lines MCF7 and MDAMB231.It caused G0/G1 phase block of cell cycle and reduced the rate of S phase of breast cancer cells. ConclusionCDAⅡ has remarkable effect of anticellproliferation and can induce cell cycle block of G0/G1 on breast cancer cells. This results provide experimental bases for the treatment of breast cancer with CDAⅡ.