Abstract: Objective: The aim of this study was to explore the effect of natto lipopeptide on human breast cancer MCF-7 cells. Method: After acid precipitation, organic solvent extraction and activated carbon adsorption, natto lipopeptide was extracted and purified from natto fermentation broth; the anti- proliferation activities of natto lipopeptide against human breast cancer MCF-7 cells was assessed by MTT assays, and the rate of apoptosis and cell cycle was detected by flow cytometry. Results: Natto lipopeptide could inhibit the proliferation of human breast cancer MCF-7 cells significantly, and with the concentration of the natto lipopeptide increased, the inhibition ratio of MCF- 7 cells increased. The IC 50 of natto lipopeptide was 3.68μg /mL. Flow cytometry analysis also demonstrated that natto lipopeptide could induce apoptosis of MCF- 7 cells and caused cell cycle arrest at S p hase.Conclusion: Natto lipopeptide could inhibit the proliferation of human breast cancer MCF- 7 cells and induce its apoptosis significantly.