Surface epithelial tumors form two thirds of ovarian neoplasms. Histologic types include serous, mucinous, endometrioid, clear cell, transitional cell, squamous, mixed, and undifferentiated. Each type can be classified as benign, borderline, and malignant. P53, a tumor suppressor gene implicated in the pathogenesis of ovarian tumors, is negatively regulated by MDM2 proto-oncogene. Overexpression of MDM2 protein results in an effect similar to the mutational inactivation of P53. The aim of this study is to examine the immunohistochemical expression profiles of MDM2 oncogene protein in the ovarian serous and mucinous epithelial tumors (benign, borderline and malignant) and to investigate the possible use of MDM2 oncogene in their diagnosis. This study included forty five paraffin blocks of ovarian tumor cases. The cases were subdivided into fifteen cases of benign cystadenomas (5 serous &10 mucinous), fifteen cases of borderline tumors (11 serous& 4 mucinous) and fifteen cases of cysadenocarcinomas (9 serous & 6 mucinous). All the studied benign tumors cases were negative for MDM2. A percentage of 62.5% of MDM2 positive serous tumor cases belonged to the malignant category while 37.5% of them belonged to the borderline one. All MDM2 positive mucinous tumor cases were of the malignant category and there were no positive mucinous tumor cases of the borderline category. So we may suggest that MDM2 immunohistochemical study alone may not be adequate for differential diagnosis. It may be used in conjunction with other adjuvant methods and with correlation to clinicopathologic features and prognostic factors.