Abstract： Background Seprase plays an important role in malignant cell invasion and metastasis by degrading the extracellular matrix. Hcwever, its clinical significance remains largely unknown. The objective of the current study was to evaluate the expression of seprase in effusions from patients with epithelial ovarian carcinoma and its clinical values.Methods Immunohistochemistry was used to examine the expression of seprase protein in a series of 74 malignant peritoneal (n=64) and pleural (n=10) effusions from Norwegian patients with epithelial ovarian carcinoma. Additionally, 34 effusions were evaluated using the Western blotting. Nine reactive effusions, obtained from patients with benign lesions,served as a control group. Statistical analyses were carried out by Chi-square test and Kaplan-Meier method.Results In the 74 malignant effusion specimens, 57 (77.02%) were positive for seprase, while only 2 (22.22%) of the control group were positively stained (P=0.001). In the malignant effusions, 17 (22.97%), 22 (29.73%), 22 (29.73%), 13 (17.57%) had negative, weak, moderate and strong seprase protein expression, respectively. The expression of seprase protein was predominant in cytoplasm of carcinoma cells. Increased seprase protein was negatively associated with the overall survival rate of the patients (P=0.03). However, there was no significant correlation between protein expression and FIGO stage, age, histology, and histological grade. By Western blotting, 27 of the 34 effusions showed the presence of both 170-kD dimeric form and 97-KD monomeric form of seprase while only 1 of the 34 had 170-KD dimeric form,which was consistent with the results of immunohistochemistry (P=0.05).Conclusions Seprase may be involved in the development of ovarian cancer, and is a potential predictive marker for the disease.