Objective:The aim of the study was to investigate the biological character change of breast cancer cell line by inhibiting the Cyclin E expressing level.Methods:Human breast cancer cell line MCF-7 was transfected by Cyclin E siRNA vector pEGFP/CCNE2.SiRNA-induced silencing of Cyclin E was determined at RNA level and protein level,respectively.The proliferation of MCF-7 and its sensitivity to chemical therapy were measured by CCK-8 assay,while cell cycle was measured by flow cytometry(FCM).Results:The plasmid could reduce the expression of Cyclin E.The proliferation ability of MCF-7 was decreased and the sensitivity to chemical therapy was enhanced according to the inhibition of Cyclin E expression.The transfected MCF-7 was arrested at G1 phase of cell cycle.Conclusion:The inhibition of Cyclin E can decrease the breast cancer cell's growth,increase its sensation to chemical therapy and slow down its cell cycle.The Cyclin E siRNA may provide us a practical tool for further study on the gene therapy to breast cancers.