Introduction: Surface Epithelial Ovarian Tumors (SEOT) are most prevalent tumors and account for about two third of all ovarian cancers. Survival of ovarian carcinoma is poor despite optimal surgical and chemotherapeutic management. Evaluation of new diagnostic and prognostic Immunohistochem. (IHC) markers will be essential in this aspect. Aim: To evaluate quant. the profile of Human Epidermal growth factor Receptor 2 (HER2)/neu IHC expression with standard scoring system in SEOTs and their association with various clinicpathol. variables (age, laterality, CA 125 levels, histol. subtype and FIGO staging). Materials and Methods: The present ambispective study was done in the Department of Pathol., SRM Medical College Hospital and Research Center, Kattankulathur, Tamil Nadu, India, from August 2020 to August 2022 with a sample size of 166 cases. All the histopathol. samples of SEOT during the study period from August 2020 to August 2022 (prospective) and all borderline, malignant and few benign cases from June 2016 to August 2020 (retrospective) were also included in the study. Cases for which slides and blocks were not available and patient treated with neoadjuvant chemotherapy or radiotherapy were excluded in the study. For prospective cases after getting clin. history and Cancer Antigen 125 (CA 125) level, specimens were fixed, processed and Haematoxylin and Eosin (H&E), IHC staining was done as per standard lab protocol, for retrospective cases clin. history, CA 125 levels, pathol. diagnosis and tissue blocks were retrieved, IHC performed and finally both prospective and retrospective cases HER2/neu IHC expression association was studied related to clinicopathol. parameters. Results: Out of total sample, SEOT was the most common (n = 184, 76.98%) tumor cases, followed by germ cell tumors (n = 42, 17.57%) cases and least common was sex cord stromal tumor (n = 13, 5.43%). HER2/neu had higher IHC expression in malignant tumors and showed statistically significant pos. association with age (p-value = 0.001), CA 125 level (p-value-0.001), and histol. diagnosis (p-value <0.001), but there is no significant association with size of tumor (p-value = 0.786), parity (p-value = 0.717), laterality (p-value = 0.514) and the International Federation of Gynaecol. and Obstetrics (FIGO) grading (p-value = 0.274). Conclusion: Malignant tumors had high HER2/neu IHC expression, thus emphasizing its carcinogenic role and helps in the diagnostic differentiation of benign and borderline tumors with malignant potential from actual malignant tumors and can be a therapeutic target in future.