Colonic diverticulitis is one of the most common gastrointestinal diseases. There are several complications in colonic diverticulitis, such as stenosis, perforation, and abscess. Stenosis is a rare complication and can cause bowel obstruction. We report a case of colonic diverticulitis complicated by stenosis causing bowel obstruction. A 66-year-old Japanese man was referred to our hospital for abdominal pain. Computed tomography (CT) scans showed the presence of diverticula, concentric wall thickening, and pericolic fat stranding in the descending colon. He was diagnosed with descending colon diverticulitis. His abdominal pain improved with fasting and intravenous antibiotics. However, after three months, diverticulitis complicated by stenosis occurred in the descending colon. The stenosis was severe and was treated with left hemicolectomy. Histologic examination revealed diverticula, chronic inflammation, and fibrosis in the stenosis, with no malignancy. Stenosis caused by colonic diverticulitis can cause bowel obstruction. Conservative treatment may lead to recurrence, and surgical treatment is preferable.