Recently, the transcription factor SOX11 has gained extensive attention as a diagnostic marker in a series of cancers. However, to date, the possible roles of SOX11 in breast cancer has not been investigated. In this study, immunohistochemical staining for SOX11 was performed for 116 cases of breast cancer. Nuclear SOX11 was observed in 42 (36.2%) and cytoplasmic SOX11 in 52 (44.8%) of breast cancer samples. Moreover, high expression of cytoplasmic and nuclear SOX11 was associated with clinicopathological factors, including earlier tumor grade, absence of lymph node metastasis and smaller tumor size. Kaplan-Meier survival curves demonstrated high nuclear SOX11 expression to be associated with more prolonged overall survival than those with low expression and it could be an independent predictor of survival for breast cancer patients. It is worthwhile to note that cytoplasmic SOX11 was not correlated with prognosis of breast cancer patients. These data suggest the possibility that nuclear SOX11 could be as a potential target for breast cancer therapy.