Background: Tegoprazan is a novel potassium-competitive acid blocker used to treat acid-related disorders. Aim: To compare tegoprazan 25 mg with lansoprazole 15 mg as maintenance therapy in healed erosive oesophagitis (EE). Methods: In this phase 3, double-blind, multi-centre study, patients with endoscopically confirmed healed EE were randomised 1:1 to receive tegoprazan 25 mg or lansoprazole 15 mg once daily for up to 24 weeks. The primary efficacy endpoint was the endoscopic remission rate after 24 weeks. The secondary efficacy endpoint was the endoscopic remission rate after 12 weeks. Safety endpoints included adverse events, clinical laboratory results and serum gastrin and pepsinogen I/II levels. Results: We randomised patients to tegoprazan 25 mg (n = 174) or lansoprazole 15 mg (n = 177). Most had mild EE (Los Angeles (LA) grade A: 57.3%, LA grade B: 37.3%). The endoscopic remission rate after 24 weeks was 90.6% with tegoprazan and 89.5% with lansoprazole. Tegoprazan was not inferior to lansoprazole for maintaining endoscopic remission at 24 weeks and 12 weeks. In subgroup analysis, tegoprazan 25 mg showed no significant difference in maintenance rate according to LA grade (p = 0.47). The maintenance effect of tegoprazan was consistent in CYP2C19 extensive metabolisers (p = 0.76). Increases in serum gastrin were not higher in tegoprazan-treated than lansoprazole-treated patients. Conclusions: Tegoprazan 25 mg was non-inferior to lansoprazole 15 mg in maintenance of healing of mild EE. In this study, tegoprazan had a similar safety profile to lansoprazole.