Abstract: Objective To investigate the effects of AZD2281 on proliferation and apoptosis of human breast cancer cell MDA-MB-231 in vitro and the possible mechanisms. Methods Different concentrations of AZD2281（2.5, 5, 10 nmol/L） were used to treat MDA-MB-231 cells for 24，48，72 h， and its effects of time and dose were observed. Cell proliferation inhibition rates were measured by MTT assay. The flow cytometry was used to analyze cell-cycle distribution and cell apoptosis. The western blotting was used to detect the expression levels of Bcl-2 and caspase-3. Results The proliferation of MDA-MB-231 cells was inhibited by AZD2281 in a dose-and time-dependent manner. The cell was arrested in the G0/G1 phase by AZD2281 treatment after 24 h， and the cell apoptosis was induced in a dose-dependent manner. AZD2281 could down-regulate the protein expression of Bcl-2 level after treatment with AZD2281 but up-regulate the protein expression level of caspase-3 protein. Conclusion AZD2281 can inhibit the proliferation of human breast cancer cell MDA-MB-231 and induce its apoptosis by down-regulating the expression of Bcl-2 protein and up-regulating the expression of caspase-3 protein.