Ski-interacting protein (SKIP) is a nuclear hormone receptor-interacting cofactor, interactions with the proto-oncogene Ski, appears to modulate a number of signalling pathways involved in control of cell proliferation and differentiation, and may play a critical role in oncogenesis. In the present study, to investigate the potential roles of SKIP in breast cancer, expression patterns, interaction and the correlation with clinical/prognostic factors of SKIP and Ki-67 were examined among patients with breast cancer. Immunohistochemistry and Western blot analysis were performed for SKIP in 85 breast carcinoma samples. The data were correlated with clinicopathological features. The univariate and multivariate survival analyses were also performed to determine their prognostic significance. We found that SKIP was over expressed in breast carcinoma as compared with the adjacent normal tissues. High expression of SKIP was positively associated with histological grade (P = 0.01) and Ki-67 (P = 0.004). Univariate analysis showed that SKIP expression was associated with a poor prognosis (P = 0.006). While in vitro, following release of breast cancer cell lines from serum starvation, the expression of SKIP was up-regulated, whereas p27 was down-regulated. In addition, we employed small interfering RNA (siRNA) technique to knock down SKIP expression and observed it effects on MDA-MB-231 cells growth. SKIP depletion by siRNA inhibited cell proliferation, blocked S phase and decreased cyclin A and cyclin B levels. On the basis of these results, we suggested that SKIP overexpression was involved in the pathogenesis of breast cancer, which might serve as a future target for breast cancer.