The objective of this study was to determine the potential of osteopontin (OPN) and OPN + CA125 (cancer antigen 125) combination in differential diagnosis of the ovarian cancers and non-malignant ovarian disease. Serum and plasma samples were obtained preoperatively from 79 women undergoing surgery for pelvic mass; 48 of them had ovarian carcinoma, and 31 had benign cyst. The samples were analyzed for the levels of OPN and CA 125 (using ELISA and CMIA methods) and then compared with the final pathologic results. The median plasma level of OPN in patients with benign and malignant cysts was 356.33 ng/ml and 865.15 ng/ml, respectively (p < 0.001). Receiver operating characteristic (ROC) analysis for plasma OPN revealed the area under the curve (AUC) of 0.838. At the predefined specificity of 90%, OPN showed sensitivity of 62.5%, whereas the combination of OPN + CA125 reached 74.9% at the same specificity.