With the wide use of colonoscopy and develoment of technology, colon tumors and colon polyps are being found frequently and for the treatment of colon polyp, endoscopic polypectomy is used at present. The most common complications of endoscopic colon polypectomy are hemorrhage and perforation. Colon perforation is an abdominal emergency with high mortality. When colon perforation happens, surgical resection was being used at past. But when colon perforations are resulted from therapeutic colonoscopy, devoid of down stream obstacles with a perfectly prepared colon, and the patient's general condition is satisfactory, colon porforation is successfully treated by conservative measures. But, in delayed diagnosed perforation endoscopic treatment is controversial yet. We report here a case which sustained iatrogenic delayed diagnosed perforation of the sigmoid colon caused by polypectomy that was successfully treated by endoscopic clip therapy. (Korean J Gastrointest Endosc 2001;23:240-244)