Abstract: Objective :To study the combined effects of quercetin (QUE) and (aide (OCT) on proliferation in human breast cancer cells. Methods : a Human breast carcinoma cell line MDA-MB-231 was treated with five different concentration of QUE and OCT in vitro, optical density (OD) was evaluated by methyl thiazolyl tetrazolium (MTT) assay. b) The cell line was treated with half of 50% inhibited concentration(ICSO) of QUE and OCT in vitro, distribution of cell cycle was determined by flow cytometry, and expression of telomerase was analyzed by immunocytochemical staining. Results :The fa of MDA-MB-231 cells that were treated with five concentration of QUE and OCT was 1.45%, 3.63%, 8.32%, 13.14% and 85.78%, respectively, and all the combination indices (CI) were lower than 1. The cell cycle was blocked in Go-G, (P<0.01) and the expression of telomerase was downregulated by QUE cooperated with OCT (P<0.01). Conclusions :QUE combine with OCT can inhibit the proliferation of MDA-MB-231 cells, and the antitumor mechanism is associated with the arrest of cell cycle and the inhibition of telomerase activity.