BACKGROUND: Management of antithrombotic agents during endoscopic treatment changed after the publishing of -Japan Gastroenterological Endoscopy Society guidelines for gastroenterological endoscopy in antithrombotic drug users (GL-2012). OBJECTIVES: We aimed to evaluate the effect of implementing antithrombotic agent management guidelines (GL-2012) on postoperative bleeding after endoscopic submucosal dissection (ESD) for early gastric cancer (EGC) and on the prevention of thromboembolic events. METHODS: A total of 1,264 patients who underwent ESD for EGC at Kyoto Prefectural University Hospital between June 2002 and March 2017 were enrolled and divided into 2 groups: 621 patients before the publication of GL-2012 (Pre-GL group) and 643 patients after (Post-GL group). Relationships between postoperative bleeding and various clinicopathological factors in each group were investigated through propensity score-matching analysis. RESULTS: In the Pre-GL group, antihypertensive agent use (p < 0.01) and upper third of the stomach (p < 0.01) were significantly related to postoperative bleeding in univariate analysis. Antihypertensive agent use (OR 4.6, 95% CI 1.6-12.8) and upper third of the stomach (OR 4.9, 95% CI 1.8-13.4) were significantly related to postoperative bleeding in multivariate analysis. In the Post-GL group, antihypertensive agent use (p < 0.01), dual antiplatelet agents use (p < 0.01), anticoagulant agents use (p < 0.01), and heparin replacement therapy (p < 0.01) were significantly related to postoperative bleeding in univariate analysis. Antihypertensive agent use (OR 3.4, 95% CI 1.1-9.6), dual antiplatelet agents (OR 12.3, 95% CI 2.4-63.0), and heparin replacement therapy (OR 10.2, 95% CI 2.5-41.5) were significantly related to postoperative bleeding in multivariate analysis. CONCLUSIONS: The adherence to GL-2012 might reduce risk of thromboembolic events. On the other hand, dual antiplatelet agents therapy and heparin replacement therapy were the new independent risk factors for ESD postoperative bleeding in EGC after GL-2012. Especially as for heparin replacement therapy, uninterrupted warfarin or a temporary short interruption of direct oral anticoagulants without heparin replacement therapy might be recommended rather than heparin replacement therapy.