Recently, traction‐assisted endoscopic submucosal dissection (ESD) using a clip and thread was reported as useful for treating lesions in the esophagus, stomach, and colorectum in terms of shortening the duration of the procedures and reducing the risk of intraoperative perforation. However, no traction method using the thread and clip for duodenal ESD as described in this article has been reported to date. We report a case in which traction‐assisted ESD using dental floss and a clip was successfully performed on a huge superficial nonampullary duodenal epithelial tumor accompanied by severe fibrosis caused by preoperative biopsies. A 65‐year‐old woman had a 55‐mm flat‐elevated tumor in the second part of the duodenum. Severe fibrosis of the submucosal layer was expected due to repeated biopsies at the same site by the patient’s previous endoscopist. We selected ESD for this lesion, and the initial incision was started from the side proximal to the lesion, but it was difficult to insert the scope under the submucosal layer directly beneath the biopsy scar. Therefore, traction with an endoclip and dental floss was performed to lift the lesion. Excellent traction allowed safe resection of the fibrotic part under accurate visual observation. Finally, the lesion was resected en bloc without adverse events. Traction‐assisted ESD using dental floss and a clip is likely to be an effective adjunctive technique for quick, safe, and successful resection of lesions in the duodenum on which it is difficult to perform ordinary ESD and that have a high probability of intraoperative perforation and massive bleeding.