BACKGROUND Ovarian cancer is the leading cause of death in women with gynecological cancers. Ovarian Brenner tumor (BT) is an extremely rare type of epithelial ovarian cancer that accounts for about 1-3% of all ovarian cancers. Herein, we report a rare case of ruptured malignant ovarian Brenner tumor. CASE REPORT A 39-year-old P0A0 woman came to the Emergency Department (ED) with abdominal pain and tenderness. Perforated appendicitis was initially suspected and an emergency laparotomy was performed by the General Surgery Department. Then, a 25×20×15 cm grayish cystic mass originating from the right adnexa was found. We consulted intraoperatively with the Gynecology Oncology Department and decided to perform complete surgical staging. Histopathological examination confirmed the diagnosis of malignant Brenner tumor (MBT). The patient was then given adjuvant chemotherapy with a paclitaxel carboplatin regimen. In this case report, we present our case along with a review of the current literature regarding the diagnosis and therapy of malignant Brenner tumor. CONCLUSIONS Ovarian MBT is an extremely rare ovarian cancer. Diagnosing MBT can be challenging as there are no clinical, laboratory, or imaging features typical for it. Surgery is the mainstay treatment in MBT cases. The role of adjuvant chemotherapy in MBT is still being debated.