To clarify the role of claudin-4 in endometrial tumorigenesis and to explore whether claudin-4 could be a potentially useful agent in the treatment of endometrial carcinoma, the expression of claudin-4 in endometrial carcinoma was investigated. The relationship between therapy with antineoplastic agents and the expression of claudin-4 was also analyzed using an endometrial carcinoma xenograft model. The expression of claudin-4 in endometrial endometrioid adenocarcinoma (EEC) and normal human endometrial tissue was determined using immunohistochemistry and real-time PCR. Ninety female BALB/c nu/nu mice were transplanted with Ishikawa endometrial cancer cells. The mice were divided into three groups with different intraperitoneal treatments: cisplatin, paclitaxel or saline solution. After the observation period tumors were extracted and stained with monoclonal antibody against claudin-4. The mRNA expression of claudin-4 was also detected using real-time PCR. Expression of claudin-4 was significantly increased at both protein and mRNA levels in the EEC group compared with the group of normal cyclic endometrium. In the study of Ishikawa xenografts, no significant changes in tumor volume and claudin-4 expression were shown in the paclitaxel group compared with the control group. A significant reduction of tumor growth and a significant decrease in claudin-4 expression were observed in the cisplatin group. These results demonstrate that claudin-4 is strongly expressed in EEC. Claudin-4 is a useful biomarker in the treatment of patients with endometrial carcinoma.