Abstract: Objective To study the effect of Angiotensin Ⅱ on cell proliferation and the activity of matrix metalloproteinase in breast cancer cells.Methods MCF-7 cells were cultured in vitro and stimulated with Angiotensin Ⅱ and/or Losartan.The viability of cells was tested by MTT assay.We used RT-PCR to detect the mRNA level of MMP-2,MMP-9,TIMP-1 and TIMP-2.The activity of MMP-2 and MMP-9 were measured by gelatin zymography.Results Angiotensin Ⅱ stimulated the growth of breast cancer cells in a dose-and time-dependent manner.Moreover,the expressions of MMP-2 and MMP-9 mRNA were significantly up-regulated by Angiotensin Ⅱ.The expressions of TIMP-1 and TIMP-2 mRNA were significantly down-regulated by Angiotensin Ⅱ.In addition,Angiotensin Ⅱ significantly enhanced the activity of MMP-2 and MMP-9.Angiotensin Ⅱ had a maximal response with 100nM(P＜0.05).Losartan significantly decreased the effect of Angiotensin Ⅱ on matrix metalloproteinase.Conclusion In summary,our study can support the concept that Angiotensin Ⅱ/ Angiotensin Ⅱ type 1 receptor(AT1R)signaling can regulate the expression of matrix metalloproteinase.Losartan can significantly decrease the effect of Angiotensin Ⅱ on matrix metalloproteinase.Therefore,targeting Angiotensin Ⅱ/ Angiotensin Ⅱ type 1 receptor(AT1R)signaling could be a novel therapeutic for breast cancer.