A case of a 70-year-old Egyptian postmenopausal woman presenting a Brenner's tumor associated with mucinous cystadenoma weighing 20.7 kg is reported here. Patient was admitted in our hospital with abdominal pain of one-month duration. On abdominal ultrasound, a huge heterogeneous mass was found to encompass the whole abdomen. At laparotomy, a giant, right heterogeneous mass was encountered and removed intact by right salpingo-oophorectomy. On the seventh postoperative day, she was discharged without any problem. Her pathology report disclosed a 52 x 41 x 36 cm, partially solid, partially cystic mass diagnosed as benign Brenner's tumor with mucinous cystadenoma weighing 20.7 kg. This is the largest ovarian mass that is ever reported in our hospital and one of the largest among the reported cases in the literature.