INTRODUCTION: X842 is a new type of gastric acid-suppressing agent with a rapid onset of action and a long duration of effect. We aim to investigate the efficacy and safety of different doses of X842 vs lansoprazole in the treatment of patients with erosive esophagitis (EE). METHODS: This phase 2 study included 90 patients with EE (Los Angeles grades A-D) who were randomized (1:1:1) to receive oral low-dose X842 (50 mg/d, n = 31), high-dose X842 (100 mg/d, n = 31), or lansoprazole (30 mg/d, n = 30) for 4 weeks. The main efficacy end point was the EE healing rate, which was the proportion of patients who achieved endoscopic healing after 4 weeks of treatment. RESULTS: For intention-to-treat analysis, the EE healing rates at 4 weeks were 93.6% (29/31), 79.3% (23/29), and 80.0% (24/30) for the X842 50 mg, the X842 100 mg, and the lansoprazole 30 mg groups. For per-protocol analysis, the EE healing rates at 4 weeks were 93.6% (29/31), 80.8% (21/26), and 82.1% (23/28) in the 3 groups, respectively. The EE healing rate did not significantly differ among the 3 groups in either the intention-to-treat ( P = 0.2351) or per-protocol ( P = 0.3320) analysis. The incidence of drug-related treatment-emergent adverse events did not differ among groups. No severe drug-related treatment-emergent adverse events occurred in the X842 group. DISCUSSION: Our findings confirmed that X842 had efficacy and a favorable safety profile similar to those of lansoprazole. Therefore, X842, a novel potassium-competitive acid blocker, is expected to become a promising therapeutic agent for EE.