Data of 55 patients with duodenal mass lesions treated by endoscopic submucosal dissection (ESD) were retrospectively analyzed. Risk factors of delayed bleeding after ESD were explored by univariate analysis and multivariate unconditional logistic regression analysis. Duodenal delayed bleeding occurred in 5 patients (9.09%). No closure treatment under endoscopy(P=0.035) was significantly different between the delayed bleeding group and the non-delayed bleeding group. Multivariate non-conditional logistic regression showed no closure treatment under endoscopy was an independent risk factor for delayed bleeding after ESD in duodenal mass lesions (P=0.029，OR=0.079，95%CI: 0.008-0.776). Patients older than 60 years and who did not take endoscopic closure treatment have higher incidences of delayed bleeding after ESD. No closure treatment under endoscopy is directly related to postoperative delayed bleeding.