Background: Ovarian cancer especially the epithelial type, is a major cause of female morbidity and mortality worldwide. So, there is a great need for better diagnostic tools that can improve the histological diagnosis and predict the outcome by using immunohistochemical procedures. Aim of the work: To evaluate the immunohistochemical expression of Insulin-like Growth Factor II m-RNA-binding Protein 3 (IMP3) in benign, borderline and malignant serous ovarian tumors and correlate this expression with some clinicopathological parameters. Methods: This cross-sectional study was conducted retrospectively on 63 formalin fixed, paraffin embedded tissue blocks of serous ovarian tumors from Pathology department, Zagazig University from 2016 to 2019. Immunohistochemical staining using anti-IMP3 antibodies was done using streptavidin-biotin immunoperoxidase technique. The relationship between the staining intensity and percentage of positively stained cells and clinicopathological factors were statistically analyzed. Results: IMP3 expression was detected in all serous borderline tumors (SBTs), 91.4% of malignant cases and 12.5% of benign cases. IMP3 intensity and percentage of positive stained cells were correlated with higher tumor grades and stages (P <0.001). A significant correlation was found between IMP3 expression and patient's age (P <0.001). Conclusion: IMP3 expression was increased from benign to borderline to malignant ovarian serous tumors, so it may have a role in carcinogenesis of ovarian serous tumors. IMP3 strong expression was expressed in higher stages and high grade serous carcinomas, so it can be used as bad predictive marker.