Abstract: OBJECTIVE To investigate the effect of ginsenoside Rg3 on cell proliferation and invasion of estrogen receptor(ER) positive breast cancer MCF-7 cell line and the potential mechanism. METHODS The proliferation of MCF-7 cell was detected by MTT assay. Cell cycle and apoptosis rate were analyzed by flow cytometry. The effect on cell invasion was assayed by using the transwell methods. The expression of MMP-9 mRNA in MCF-7 cell was analyzed with the RT-PCR. RESULTS Compared with the control group, ginsenoside Rg3 could significantly inhibit the proliferation of MCF-7 breast cancer cells. The cell cycle of MCF-7 was also changed after treated with the ginsenoside Rg3. The percentage of cells in G₀/G₁ and S phase were decreased, whereas the percentage of cells in G₂/M was increased significantly. ginsenoside Rg3 could also induce the MCF-7 cell apoptosis and decrease the index of cell invasion on a time and dose-depended manner. Meanwhile, ginsenoside Rg3 could significantly suppress the expression of MMP-9 mRNA on MCF-7 cell(P<0.05). CONCLUSION ginsenoside Rg3 could inhibit the proliferation and invasion of breast cancer MCF-7 cell line, the underlying mechanism may be related with the inhibitory effect of ginsenoside Rg3 on MMP-9 mRNA expression in MCF-7 cell.