Ubiquitination is essential for various biological processes, such as signal transduction, intracellular trafficking, and protein degradation. Accumulating evidence has demonstrated that ubiquitination plays a crucial role in cancer development. In this report, we examine the expression and function of ubiquitin-conjugating enzyme E2S (UBE2S) in breast cancer. Immunohistochemical analysis revealed that UBE2S is highly expressed in breast cancer. The depletion of UBE2S by siRNA induced disruption of the actin cytoskeleton and focal adhesions. Interestingly, phosphorylation of FAK at Tyr397, which is important for the transduction of integrin-mediated signaling, was significantly reduced by UBE2S knockdown. We also show that UBE2S knockdown suppressed the malignant characteristics of breast cancer cells, such as migration, invasion, and anchorage-independent growth. Our results indicate that UBE2S could be a potential target for breast cancer treatment.