A 74-year-old man was referred to our hospital for abdominal pain and fever. He had hypertension. He underwent surgery for rectal cancer 7 years ago and again for liver metastasis 2 years ago. He had a recurrence of liver metastasis and peritoneal dissemination a year ago and received chemotherapy (XELOX + bevacizumab). His blood tests showed an elevated white blood cell count of 15,300/mm3. A contrast-enhanced computed tomography (CT) of the abdomen showed fluid collection like an abscess surrounding the gallbladder and hepatic flexure colon. The patient was diagnosed with colonic perforative peritonitis, and he underwent emergency surgery. On laparotomy, the abscess was located outside of the hepatic flexure colon and necrosis was found on the gallbladder after mobilization of the ascending colon. The neck of the gallbladder and near the hepatoduodenal ligament was too severely inflamed to dissect. The hepatic flexure colon was part of the abscess wall, and resection was needed. For diagnosis of peritonitis caused by cholecystic perforation, a subtotal cholecystectomy and right hemicolectomy was performed. The gallbladder was removed at the neck, and the mucosa of the gallbladder neck was necrotic or detached. Therefore, the stump of the gallbladder was closed by primary sutures without cauterizing the mucosa. An abdominal drainage tube was placed into the gallbladder bed. The total operative time was 318 min, and the estimated blood loss was 1369 ml. On postoperative day (POD) 6, bile was detected from the abdominal drainage tube. Contrast examination of the drainage tube enabled visualization of the neck of the gallbladder, and bile leakage from the gallbladder stump was revealed. On POD 29, bile leakage was still a problem and an endoscopic nasobiliary drainage (ENBD) tube was inserted. Imaging from the ENBD tube revealed the leakage was from the gallbladder stump. After insertion of the ENBD tube, the volume from the abdominal drainage tube decreased and became less biliary, but a white transparent liquid was continuously obtained 100 ml or more per day. On POD 57, imaging from the ENBD tube enabled visualization of the remnant gallbladder and it revealed that the gallbladder stump and common bile duct were connected. The liquid seemed to be secreted from the mucosa of the remnant gallbladder. We planned to use argon plasma coagulation (APC) to cauterize the gallbladder mucosa through the fistula of the abdominal drainage tube. The patient was given a full explanation of the procedure, and written informed consent was obtained. All procedures used in this case report were approved by the ethical committee of our hospital. APC cauterization was performed three times on PODs 64, 71, and 82. It was a video-assisted procedure using a CHF-U cholangioscope (Olympus Co., Tokyo, Japan), and the diameter of the scope was 5.2 mm. APC was performed with high frequency generator (VIO 300D), an automatically regulated argon source (APC2), and flexible APC probes (all manufactured by ERBE Elektromedizin, Tuebingen, Germany). We used argon gas at a flow rate of 1.5–2 L/min and a high-frequency arc output of 50–60 W. Cholangioscopy showed that the membrane of the remnant gallbladder was widely recognized, and entrance to the cholecystic duct was found in the back. Because the safety of APC cauterization of the gallbladder mucosa had not previously been reported, we initially tried to cauterize the membrane not entirely but randomly at several points. Upon the second cauterization, we found sclerosis in the region that was previously cauterized. There were no complications, and the second region was cauterized all over. A very small region of the membrane was cauterized on POD 82. The abdominal drainage volume decreased over time after removal of the ENBD tube on POD 87 and the abdominal drainage tube on POD 90. He was discharged on POD 95, and 7 months after the surgery, a follow-up CT scan showed the remnant gallbladder was atrophic.