A 60-year old woman was examined by a local physician for the chief complaint of bloody stool, and underwent colonoscopy. A laterally spreading tumor 〔IIa (LST-G) 〕 measuring approximately 10 cm along the major axis and occupying approximately 5/6th of the circumference of the rectum was identified, and the patient was referred to our department. Although submucosal invasion was suspected, endoscopic submucosal dissection (ESD) was performed as per the desire of the patient ; en-bloc resection of the tumor was performed, with dissection of almost the entire circumference of the rectal mucosa. After the ESD, steroid suppositories were administered for 26 days to prevent stenosis. However, one month after the ESD, colonoscopy revealed cicatricial stenosis at the resection site, with inability to pass the scope through the stenotic site. Histopathological examination indicated pT1b (4,000 µm) adenocarcinoma in adenoma. Therefore, laparoscopic low anterior resection was performed 2 months after the ESD. Histopathological examination did not indicate residual cancer or lymph node metastasis, however, the fibrosis had extended to the muscularis propria at the scar site, which was considered to be the cause of the stenosis. Post ESD stenosis of the rectum is considered to be rare. We carried out histopathological investigation to identify the cause of the stenosis in a patient who presented with bowel stenosis after ESD for a large rectal tumor.