Objective: AT-rich interactive domain 1A (ARID1A) or BAF250a protein, which is encoded by tumor suppressor ARID1A gene, is involved in chromatin remodeling. The aim of this study is to investigate the association between tissue ARID1A expression and ovarian epithelial tumors. Material and Methods: ARID1A expression was studied in a total of 137 formalin-fixed, paraffin-embedded specimens of ovarian epithelial tumors. Results: Statistically, normal ARID1A expression was determined in borderline and malignant serous tumors (p < 0.001). On the contrary, the decreased levels of ARID1A expression were found in endometrioid and mucinous carcinomas, as well as in benign serous tumors (0.033). Conclusions: This study demonstrated the presence of a relationship between ARID1A expression deficiency and pathogenesis of mucinous and endometrioid carcinomas. Contrary to previous studies, ARID1A expression was normal in borderline serous tumors similar to serous carcinomas. Based on these results, it can be suggested that pathogenesis of borderline serous ovarian tumors is closer to high-grade than to low-grade serous carcinomas.