Obstructive colitis is an acute condition caused by colorectal strictures and requires a combination of therapeutic strategies, including surgery, endoscopic interventions, and medications. Here, we describe the case of a 69-year-old man who developed severe obstructive colitis owing to diverticular stenosis of the sigmoid colon. We immediately performed endoscopic decompression to avoid perforation. The mucosa of the dilated colon appeared black, suggesting severe ischemia. We considered surgical total colectomy owing to the extensive colitis. However, considering the invasiveness of the emergent surgery, we adopted a conservative approach as enhanced computed tomography demonstrated colonic dilation with maintained blood flow in the deeper layer of the colonic wall and no signs of colonic necrosis, such as peritoneal irritation sign or elevation of deviation enzymes, were observed. Moreover, the patient preferred a conservative approach, and surgeons in our team agreed with this conservative approach. While relapses of colonic dilation occurred several times, antibiotic treatment and repeated endoscopic decompression successfully suppressed the dilation and systemic inflammation. The colonic mucosa healed gradually, and we performed a colostomy without resecting a large portion of the colorectum. In conclusion, severe obstructive colitis with maintained blood flow can be treated with endoscopic decompression instead of emergent resection for a wide portion of the colorectum. Moreover, endoscopic images of improved colitic mucosa obtained through repeated colorectal procedures are rare and noteworthy.