Introduction: Non-Hodgkin's lymphoma in the genital system is uncommon and ovary is one of the most common sites of involvement. Ovarian involvement in non-hodgkin's lymphoma is often secondary and is a part of the systemic involvement. Primary and localized ovarian involvement is uncommon and occurs in less than 10% of cases. In this study, a rare case of primary ovarian non-Hodgkin's lymphoma is presented. Case presentation: The patient was a 64-year-old woman with a history of hysterectomy and postmenopausal bleeding that referred to the academic hospital of Mashhad University of Medical Sciences. On ultrasound and CT scans, solid cystic foci were found between the bladder and rectum, consistent with the location of the cervix and uterus. Subsequent evaluations confirmed histological and immunohistochemical diagnosis of ovarian non-Hodgkin's lymphoma. Conclusion: Ovarian lymphoma is one of the differential diagnoses that should be considered in the pelvic masses.