A 67-year-old woman presented with abdominal distension and difficulty in defecation. She had a huge mass in the left lower abdomen and hyperamylasemia with normal pancreatic-type amylase (P-AMY). Nuclear magnetic resonance and computed tomography scan revealed a huge pelvic mass, but the origin of mass wasn't certain. After discussion with the multidisciplinary team, ultrasonography guided pathological biopsy of the mass was done. Pathological biopsy showed that the mass was poorly differentiated adenocarcinoma, which may be originated from ovary. Patient was on neo-adjuvant chemotherapy. After one and a half months of chemotherapy, the patient developed colorectal-reproductive system fistula with hyperpyrexia. Laparatomy with resection of mass, sigmoid colon, left ovary and part of uterus, proximal colostomy with closure of the distal rectum and end to end anastomosis of left ureter with DJ tube drainage (left ureter invaded by tumor confirmed intra operation) was done. Operative finding: Fistula between sigmoid colon and uterus through the tumor.