Objective:To study the effect of tamoxifen(TAM) and megestrol acetate(MA) on breast cancer cell line MCF-7. Methods:Estrogen receptor(ER)-positive MCF-7 human breast cancer cell line was treated by TAM or MA alone,or in combination in vitro. Cell proliferation was evaluated by MTT assay. Distribution of cell cycle and rate of apoptosis were determined by flow cytometry(FCM). Results:TAM can inhibit MCF-7 cells proliferation and induce its apoptosis. The cells were arrested in G0/G1 phase;small doses of MA had no significant effect on apoptosis,G0/G1 phase cells increased. When TAM combined with MA,the inhibition effect on proliferation and apoptosis were enhanced. Conclusion:TAM can inhibit MCF-7 cells proliferation and induce its apoptosis. The therapy effect can be improved when two drugs are combined.