The aim of this study was to investigate the efficacy and safety of imeglimin, the first in a new class of oral antidiabetic agent, in Japanese patients with type 2 diabetes.This was a double-blind, randomized, parallel-group, placebo-controlled phase 3 trial in 30 sites in Japan. Eligible participants were individuals aged ≥20 years with type 2 diabetes treated with diet and exercise, stable for ≥12 weeks prior to screening, and whose HbA1c was 7.0-10.0% (53-86 mmol/mol). Patients were randomly assigned (1:1) to either oral imeglimin (1,000 mg twice daily) or matched placebo for 24 weeks. Investigators, participants, and the sponsor of the study remained blinded throughout the trial. The primary end point was the change in mean HbA1c from baseline to week 24, and the key secondary end point was the percentage of responders (according to two definitions) at week 24.Between 26 December 2017 and 1 February 2019, 106 and 107 patients were randomly assigned to treatment with imeglimin and placebo, respectively. Compared with placebo, the adjusted mean difference in change from baseline HbA1c at week 24 was -0.87% (95% CI -1.04 to -0.69 [-9.5 mmol/mol; 95% CI -11.4 to -7.5]; P < 0.0001). Forty-seven (44.3%) patients reported ≥1 adverse event in the imeglimin group versus 48 adverse events (44.9%) in the placebo group.Imeglimin significantly improved HbA1c in Japanese patients with type 2 diabetes compared with placebo and had a similar safety profile to placebo. Imeglimin represents a potential new treatment option for this population.