S100 proteins belong to the EF-hand Ca2+ -binding protein family and regulate a variety of cellular processes via interaction with different target proteins. Several diseases, including cancer and melanoma, are related to the abnormal expression of S100 proteins, which are expressed in cell- and tissue-specific manners. We investigated the expression of S100 family members in human uterine smooth muscle tumours. Expression of six members of the S100 protein family: S100A1, A4, A6, A7, A10 and A11, was found in human uterine leiomyoma and myometrium tissue, but expression of other members was not detected by RT-PCR. Real-time PCR showed that S100A11 expression was significantly increased in leiomyoma compared with myometrium. Suppression of S100A11 by small interfering RNA (siRNA) led to apoptosis, and the overexpression of S100A11 inhibited apoptosis in human uterine smooth muscle tumour cells. These findings suggest that S100A11 has an anti-apoptotic function and is related to the process of growth of human uterine leiomyoma.