The patient was a 65-year-old man. He had not defecated for a week in early December 2015, and had noticed abdominal pain and abdominaldistension from 4 days prior. The pain and distension worsened, and the patient was rush transported to our hospital. Via abdominal CT we found free air in the upper abdomen, expansion of the small and large intestines, and notably, significant intestinal tract expansion and a gas reservoir in the ascending colon. We found significant narrowing as well as hypertrophy along the entire circumference of the rectum and suspected gastrointestinal perforation due to rectal cancer ileus. Inflammation findings were abnormally high and we performed emergency surgery. We found a laceration on the ascending colon, which had expanded markedly. We elevated that location and installed a colostomy. Following surgery the patient developed mild SSI and ileus, which were alleviated through conservative treatment. A month after the operation we performed a colonoscopy and found a tumor along the entire circumference of the rectum Rs. It was diagnosed as group V tub1-2 via biopsy. We performed surgery in late January 2016(colostomy closure, laparotomy rectal low anterior resection). We are reporting a rare case where rectal cancer ileus caused perforation in the ascending colon.