Objective To study the inhibition effects of oncostatin M (OSM) gene on human breast cancer cell line(michigan cancer foundation-7,MCF-7).Methods MCF-7 cells were infected with the optimized dose of retrovirus expressing OSM.Expression of the target gene was determined by reverse transcriptionpolymerase chain reaction(RT-PCR) and enzyme-linked immunosorbent assay(ELISA).Methyl thiazolyl tetrazolium (MTT) assay was employed to examine growth inhibition effect of OSM gene on MCF-7 cells.Cell apoptosis was determined by flow cytometry.The morphologic changes of nucleus was detected by Hochest staining,in addition,the expression of apoptosis related genes in tumor cells were further detected by RT-PCR.Results OSM gene was well expressed in human breast cancer MCF-7 cell by retrovial vetor and it could significantly inhibit the growth of MCF-7 cell(MTT,P =0.0162,P ＜ 0.05) and induce its apoptosis (Annexin V/PI,P =0.02,P ＜ 0.05).Conclusion OSM gene has significant inhibitory effects on MCF-7 cells,which mechanism might be related to the upregulation of Bax and Caspase3 and the downregulation of Bcl-2.