Background: Endoscopic submucosal dissection (ESD) is accepted as a minimally invasive treatment for early gastric cancer, however, it is not widely used in the colorectum because of its technical difficulty. Objective: To determine the feasibility of using ESD for treating large superficial colorectal tumors. Patients: A total of 400 consecutive patients were treated by ESD for 405 lesions at National Cancer Center Hospital, Tokyo, Japan. Interventions: Endoscopic submucosal dissection procedures were performed using a bipolar needle knife (B‐knife) or an insulation‐tip knife (IT knife). Results: The en‐bloc resection rate was 87% and the curative resection rate was 86% among the 405 ESDs: 101 involved tubular adenomas, 255 intramucosal cancers and minute submucosal cancers, 46 submucosal deep cancers and 3 others (MALT and carcinoid tumors). The median operation time was 90 minutes and the mean size of resected specimens was 40 mm (range: 15 mm‐150 mm). Perforations occurred in 14 (3.5%) cases and postoperative bleeding in four (1%) cases, but only one perforation case needed emergency surgery because endoscopic clipping was ineffective. Limitations: Conducted at single center. Conclusions: Endoscopic submucosal dissection is a feasible technique for treating large superficial colorectal tumors because it provides a higher en‐bloc resection rate and is less invasive than surgical resection.