A 70-year-old man was admitted to the hospital for close examination of hematochezia. Endoscopic colonoscopy revealed a pediculate polyp with the longer diameter of 4cm in the descending colon. Since endoscopic resection was considered to be difficult, a portion of the descending colon was resected surgically. The polyp consisted of mucosa and submucosal tissue. A part of its surface transformed by ulceration and hyperplastic changes, however, most parts were covered with normal mucosa. Only fibrogenesis and angiogenesis were observed in the submucosal layer. On the basis of the above findings, the polyp was considered to meet the criteria for colonic muco-submucosal elongated polyp (CMSEP). In the present case, not only the mucosa and submucosal tissue but also a part of the muscularis were elongated toward the pedicle of the polyp. It is suggested that meticulous care must be exercised in performing endoscopic treatment for CMSEP.