Colonic perforation may occur as a complication of diagnostic and therapeutic colonoscopy. The risk factors for perforation after colorectal endoscopic submucosal dissection (ESD) include an inexperienced endoscopist, a large tumor size, and submucosal fibrosis. The mechanisms of perforation include unintended endoscopic resection/dissection and severe thermal injury. Here, we report a case of colon perforation that occurred after ESD with snaring of a laterally spreading tumor. The perforation was completely unexpected because there were no colorectal ESD-associated risk factors for perforation, deep dissection, or severe coagulation injury in our patient.