Schwannomas are uncommon neoplasms arising from Schwann cells of the neural sheath. Gastrointestinal schwannomas are rare, accounting for 1% of all malignant gastrointestinal tumors. Colonoscopic biopsy with immunohistochemical (IHC) staining is useful for confirming this tumor. We report on a patient with schwannoma arising from the ascending colon, which was detected by colonoscopy and endoscopic submucosal dissection was attempted. A 41-year-old man presented with abdominal discomfort. The patient was diagnosed with a subepithelial tumor on colonoscopy. He underwent endoscopic submucosal dissection. Histopathology and IHC staining confirmed that the colonic lesion was a benign schwannoma. However, the resection margin was positive. Therefore, laparoscopic ileocolectomy was performed.