AIM:To investigate the optimum period of treatment for post endoscopic submucosal dissection(ESD)ulcers.METHODS:Patients who underwent ESD for gastric cancer were randomized to two groups and treated with esomeprazole 20 mg per day for 4 wk(4W group)or 2 wk(2W group).At 4 wk after ESD,we measured the size of the artificial ulcers by endoscopy and determined the ulcer healing rate,compared with the size of the ESD specimens.This randomized controlled trial study was approved by our ethics committee and registered in the UMIN Clinical Trial Registry.RESULTS:A total of 60 consecutive patients were included in the study.All patients received rebamipide 300 mg per day for 4 wk.One patient in 2W group who showed bleeding within two weeks and received endoscopic treatment was excluded from further analysis.The numbers of patients with ulcers in the healing/scar stage in the 2W and 4W groups at 4 wk after ESD were 20/6 and 28/5,respectively,with no significant difference.The ulcer healing rate in the 2W and 4W groups were 96.1%[95%confidence interval(CI):94.6%-97.55]vs 94.8%(95%CI:92.6%-97.1%),respectively,with no statistical difference(UMIN000006951).CONCLUSION:Two-wk treatment with a proton pump inhibitor is as effective as four-week treatment for healing post ESD ulcers. AIM: To investigate the optimum period of treatment for post endoscopic submucosal dissection (ESD) ulcers. METHODS: Patients who underwent ESD for gastric cancer were randomized to two groups and treated with esomeprazole 20 mg per day for 4 wk (4W group) or 2 wk (2W group) .At 4 wk after ESD, we measured the size of the artificial ulcers by endoscopy and determined the ulcer healing rate, compared with the size of the ESD specimens. This randomized controlled trial study was approved by our ethics committee and A total of 60 consecutive patients were included in the study. All patients received rebamipide 300 mg per day for 4 weeks. One patient in 2W group who showed bleeding within two weeks and received endoscopic treatment was excluded from further analysis. numbers of patients with ulcers in the healing / scar stage in the 2W and 4W groups at 4 wk after ESD were 20/6 and 28/5, respectively, with no significant difference. The ulcer healing rate in 95% CI: 94.6% -97.55 vs 94.8% (95% CI: 92.6% -97.1%), respectively, with no statistical difference (UMIN000006951). CONCLUSION: Two-wk treatment with a proton pump inhibitor is as effective as four-week treatment for healing post ESD ulcers.