Giant ovarian mucinous cystadenoma becomes rare in the current medical practice. We report a 71-year-old post menopausal woman with complaints of severe abdomen distention since one year ago. This case was interesting because of the patient morbidly post-menopausal woman with giant ovarian mucinous cystadenoma. On physical examination, abdominal girth at pubic symphysis was 60 cm with a dull note on percussion. Her vulva, vagina, and cervix were grossly normal and on pelvic ultrasounds, examination showed a large well-defined cystic lesion of about 25× 20× 20 cm. Then we did laparotomy surgery on the patient. During the laparotomy salphyngo-oophorectomy procedure, we found a cyst that weighs 5.5 kg in the left ovary. We also found a sub-serous leiomyoma with a size of 7×7×4.5 cm. from the histopathologic examination, the result showed mucinous cystadenoma ovary and uterine leiomyoma. It can be concluded that laparotomy with giant ovarian mucinous cystadenoma is successful without any complications during pre-operative until post-operative.