Background: Ovarian serous tumors are the most common epithelial tumors in premenopausal and postmenopausal, 60% of the most common cases are ovarian cystadenoma, 25% of low grade and highgrade serous carcinoma. Tumor infiltrating lymphocytes (TILs) is used to predict the prognosis some solid tumors. SRY (sex determining region Y)-box 2 (SOX2) is a transcription factor. High SOX2 in ovarian tumors associated with reduced disease-free survival. Research Objective: To determine the relationship between SOX2 expression and TILs in patients with a diagnosis of ovarian serous tumor at the Anatomic Pathology Laboratory, USU Medical Faculty and RSUP. H. Adam Malik Medan. Materials and Methods: 39 samples histopathological slides with a diagnosis of ovarian serous tumor, slide review was performed and TILs assessed and then SOX2 immunohistochemical staining and then analyzed for correlation between variables using Eta test (p<0.001) and Somer'sd test (p=0.120). Results: The highest expression of SOX2 high was in the highgrade serous carcinoma subtype in 9 (23.1%) cases. Most cases were also found in low SOX2 expression with low iTILs in 20 (51.3%) cases and low SOX2 expression with low sTILs in 16 (41.0%) cases. There was a significant relationship between subtypes and SOX2 expression (p < 0.001) and the Somers'd correlation showed no significant relationship between SOX2 and TILs (p = 0.120). Conclusion: In this study, there was a correlation between tumor subtypes and SOX2 expression and there was no correlation between SOX2 expression and TILs in ovarian serous tumors.