Abstract: Objective To investigate the effect of quercetin on the proliferation and invasion in human breast cancer cells. Methods The proliferate capacity of human breast carcinoma cell line MDA-MB-435S was measured using tryan blue dye exclusion test, the apoptosis rate was analyzed using flow cytometry and the invasive capacity was measured using Boyden chamber invasive model after the cells were treated with different concentrations of quercetin (12.5,25,50,100 and 200μM) . Results Quercatin could inhibit the proliferation and invasion and induce apoptosis of MDA-MB-435S cells at dose dependent relationships. With 200μM of quercatin the growth and invasion of MDA-MB-435S cells were almost completely inhibited. Conclusion Quercatin could inhabit the proliferation and invasion and induce apoptosis of human breast carcinoma cell line MDA-MB-435S at dose dependent patterns, which could provide some bases for the clinical application of quercatin for breast cancer therapy in the near future．