It was suggested that the enhancer of zeste homolog 2 (EZH2) gene is a putative candidate oncogene in several types of human cancer. The potential oncogenic role of EZH2 and its clinical/prognostic significance, however, in ovarian carcinoma are unclear. In this study, EZH2 expression was examined by immunohistochemistry (IHC) in cohorts of normal and tumorous ovarian tissues. High expression of EZH2 was examined in none of the normal ovaries, in 3% of the cystadenomas, in 23% of the borderline tumors and in 50% of the ovarian carcinomas, respectively. In the ovarian carcinomas, high expression of EZH2 was positively correlated with an ascending histological grade and/or advanced stage of the disease (P < 0.05). Moreover, high expression of EZH2 in ovarian carcinoma was determined to be a strong and an independent predictor of short overall survival (P < 0.05). In ovarian carcinoma HO-8910 and UACC-326 cell lines, EZH2 knockdown by RNA interference led to a G(1) phase cell cycle arrest, reduced cell growth/proliferation and inhibited cell migration and/or invasion in vitro. In addition, EZH2 knockdown was found to reduce transforming growth factor-beta1 (TGF-beta1) expression and increase E-cadherin expression either in the transcript or in the protein levels. Furthermore, a significant positive correlation between overexpression of EZH2 and TGF-beta1 in ovarian carcinoma tissues was observed (P < 0.001). These findings suggest a potential important role of EZH2 in the control of cell migration and/or invasion via the regulation of TGF-beta1 expression, and the high expression of EZH2, as detected by IHC, is an independent molecular marker for shortened survival time of patients with ovarian carcinoma.