Abstract Introduction: Ovarian epithelial cancer is an aggressive malignancy of which Ovarian Serous Carcinoma (OSC) represents a common type. The insulin-like growth factor mRNA-binding protein 3 (IMP3) is one of mRNA-binding protein family that is overexpressed in a variety of human cancers, including ovarian carcinomas. Being associated with adverse prognostic outcome in these cancers, which makes this protein a reliable biomarker to distinguish some cancers from their benign mimetic lesions. Aim: The aim of present study was to analyse IMP3 expression in serous ovarian tumours and correlates the expression in malignant tumours with Epithelio-Mesenchymal Transition (EMT) related markers (Epithelial(E)-cadherin and vimentin) and clinicopathological factors to assess the clinical application of IMP3 in the diagnosis, prognosis and possible application in targeted therapy of such tumours. Materials and Methods: This was a cross-sectional research that was done at the departments of Pathology, Obstetric and Surgery, Zagazig and Banha Universities Hospitals, Egypt. Fifty-nine formalin-fixed paraffin-embedded specimens (including 43 cases OSC, 6 cases border line serous tumour and 10 cases benign serous cystadenoma) were collected from January 2014 to December 2018. Each case was stained immunohistochemically with IMP3, E-cadherin and Vimentin. Markers expressions were statistically analysed using SPSS software (version 19.0; SPSS, Chicago, IL). The p-values ≤0.05 was regarded statistically significant. Results: IMP3 was detected in 76.7% (33/43) of the studied OSC. IMP3 was in a significant association with advanced FIGO (International Federation of Gynaecology and Obstetrics) stage and with lymph node metastases (p=0.02 and 0.019, respectively). E-cadherin was predominantly lost in 53.5% (23/43) of the studied OSCs and was significantly associated with advanced FIGO stage (p=0.004). Vimentin was detected in 79.1% (34/43) of the studied OSCs and was in association with high grades and advanced stage (p=0.018 and 0.007, respectively). An inverse significant correlation was detected between IMP3 and E-cadherin expressions (Spearman correlation (r)=-0.480, p-value=0.001), while positive significant correlation was detected between IMP3 and Vimentin expressions (Spearman correlation (r)=0.393, p-value=0.009). Conclusion: IMP3 is an oncogene unregulated in OSC. It is a prognostic marker associated with tumour aggressiveness. Moreover, IMP3 could promote tumour invasion and metastasis via EMT in OSCs.Key words:Carcinoma, Cystadenoma, Epithelial cadherin, Epithelial-related genes, Insulin-like growth factor mRNA-binding protein 3