Introduction: Borderline Brenner tumor of the ovary is a rare entity characterized by papillary structures with a fibro-vascular core, covered by a transitional epithelium, and by the absence of stromal infiltration. It is associated, by definition, with a benign component of Brenner tumor. We introduced a case about ovarian torsion of Brenner tumor. Material&method: A fifty-one years old women came to emergency room. Her chief complain was continous lower abd. pain since 3 days ago. She has 2 babies. Her menstrual cycle finished 1 years ago. She has Diabetes mellitus and hypertension. The CT scanning was compared prior CT imagings that was taken 4 years ago. There was a calcified solid mass on Rt. ovary in prior CT, About 13x10x10cm-sized well defined multiseptated cystic lesion was added on this mass. There was small amount ascites. There was a twisted ovarian pedicle on inferior portion of mass. About 7.3x9.6x8.6cm-sized well defined mass was on Lt. adnexa. The upper portion of Rt. mass was cystic portion, and the lower portion was solid mass. There was small Lymph node on Lt. paraaortic region. It seemed the reactive lesion. The beta-hcg level was below 1.20. The AFP level was 2.32. The CEA level was 2.0. The CA19-9 level was below 2.00. The CA125 level was 20.2. After low midline incision was made. Entering abdominal cavity, the uterus was normal. Both ovary cyst was seen and The Rt. ovary was twisted for 3 times. Bilateral salpingo-oopherectomy was done. The result of frozen biopsy was both brenner tumor. Result: The pathologist's conclusion was Brenner tumor originated from both ovaries. and Ovarian cystic fluid was no definite malignant tumor cells present. Her symptom such as severe abdominal pain was disappeared after surgery. Conclusion:Further investigation is required to determine whether associated Brenner tumors found during frozen section are more highly associated with malignancy and could therefore change intraop-erative and overall decision making.