A 59-year-old man was admitted to the hospital because of an abdominal pain. On plain abdominal X-ray examination he was diagnosed as intestinal obstruction. Although an ileus tube was inserted, symptoms became worse. A cystic structure above the urinary bladder was identified by abdominal CT scan and echography. It was about 5 cm in diameter and the ileum was incarcerated in this cavity. Operation was carried out for a suspicion of intestinal obstruction due to hernia. A cyst below the navel was found to be included in a cord connecting to the urinary bladder. The ileum was incarcerated in this cavity causing hernia. The cyst including the wall of the urinary bladder and the injured ileum were resected with the operative diagnosis of strangulated ileus due to incarcerated hernia to the perforated urachal cyst. The postoperative clinical course was uneventful. The urachal cysts are often associated with infection, but uncommonly with intestinal obstruction. Only a few cases of adhesive ileus with infected urachal cyst have been reported, but this case seems the first report as causing intestinal obstruction due to hernia to the urachal cyst.