Abstract: Objective To study the best consequence of combined herceptin（HER） and adriamycin（ADM） for breast cancer during in vitro experiment and the effect of HER on ADM and its mechanism. Methods Inhibition rate of combined HER and ADM on human breast cancer cell line（MDA-MB453） and its effect on cell cycle were detected by MTT and flow cytometry（FCM）,respectively. Results The inhibition rate of combined HER and ADM was significantly higher than that of single ADM or HER therapy（P＜0.05）.The synergistic effect was achieved on breast cancer cells 12h or longer after HER therapy.Along with the change of ADM and HER sequence,the number of breast cancer cells was gradually decreased in G0/G1 and S phases,and gradually increased in G2/M phase. Conclusion Synergistic effects can be achieved on breast cancer cells when HER is used 12h after the use of ADM.The difference in sequence of HER and ADM application is related with the change of cell cycle.