The S-phase kinase-associated protein-2 (SKP2) plays a strategic role in ubiquitin-mediated proteolysis, which effects in the development of cells from inactivity to proliferative state. SKP2 is overexpressed in a variety of tumor. In this study, we used small interfering RNAs (siRNAs) to inhibit the SKP2 expression in Breast cancer cells preface investigate the role of SKP2 in breast tumorigenesis. Two Breast cancer cell lines (MCF-7 and T47D) were transfected with siRNAs targeted against SKP2. Our results showed one SKP2-siRNA specifically and efficiently reduced the levels of the SKP2 protein by 90% 48 h after transfection in MCF-7 cell line. In the transfected cells, p27 protein was accumulated inversely related to Skp2 siRNA transfected Breast cells. Skp2 siRNA inhibited the cell growth of breast cells in vitro. Moreover, Skp2 siRNA also suppressed tumor proliferation in vivo. Our results suggest that siRNA-mediated gene silencing of Skp2 can be a potent tool of cancer gene therapy for suppression of p27 degradation in breast cancer.