Primary ovarian lymphoma is extremely rare (less of 1% total ovarian malignancies). Its presentation is similar to ovarian malignancies. This is a report about primary ovarian lymphoma in a 32 years old woman. Because of clinical signs and serial sonography reports about the presence of a mass in her right ovary, laparotomy was performed. Her pathological report showed a malignant diffuse lymphoma Type B cell. The patient was referred to oncologist to perform combo-chemotherapy.