Objective To research the antitumor activity in vitro of tubeimoside on human breast cancer cell lines MDA-MB-231and MCF-7transfected with green fluorescent protein（GFP）. Methods The morphological changes of MDA-MB-231（GFP）and MCF-7（GFP）under the action of tubeimoside were observed with inverted microscope.The inhibitory effect of tubeimoside on the growth of MDA-MB-231（GFP）and MCF-7（GFP）were measured by MTT assay. Results A typical apoptosis of MDA-MB-231（GFP）and MCF-7（GFP）were shown 24hours later.MTT assay showed that tubeimoside had a strong inhibitory effect on the growth of MDA-MB-231（GFP）and MCF-7（GFP）.The inhibitory concentration 50（IC50）of MDA-MB-231（GFP）and MCF-7（GFP）was（17.03±3.22）μg/ml and（27.96±0.34）μg/ml respectively48hours later. Conclusion Tubeimoside has a strong inhibitory effect on the growth of MDA-MB-231（GFP）and MCF-7（GFP）.