Introduction: Stage-specific embryonic antigen 4 (SSEA-4) is a widely used marker to monitor the differentiation of pluripotent embryonic stem cells. Little is known about the expression pattern of SSEA-4 in solid tumors up to now. Methods: In this study, we investigated the expression of SSEA-4 in 479 cases of various degrees of ovarian epithelial lesions by immunohistochemistry, consisting of 45 normal ovarian epithelia, 110 benign serous ovarian cystadenomas, 68 borderline serous ovarian cystadenomas, 104 invasive serous ovarian carcinomas, 64 benign serous mucinous cystadenomas, 48 borderline mucinous ovarian cystadenomas, and 40 invasive mucinous carcinomas. Moreover, the association between SSEA-4 expression and clinicopathological parameters was also evaluated. Results: The expression of SSEA-4 was found to be increased from normal epithelium to benign cystadenoma and to borderline cystadenoma and adenocarcinoma in both serous and mucinous group. The loss or reduction of the expression of SSEA-4 was significantly correlated with more advanced tumor stage and poorer tumor cell differentiation. Conclusions: We therefore proposed that SSEA-4 may play a role during the oncogenesis of epithelial ovarian carcinoma and posses a tumor suppressor effect during malignancy promotion. It could be a potential therapy target in patients with epithelial ovarian carcinoma. Copyright © 2010 by IGCS and ESGO.