Introduction: The aim of this study was to evaluate the efficacy and safety of ultra-rapid lispro (URLi) versus lispro in a subgroup analysis of Japanese adults with type 2 diabetes mellitus (T2DM) from the phase 3 PRONTO-T2D trial. Methods: After an 8-week lead-in period during which patients transitioned to insulin lispro 3 times a day before main meals in association with basal insulin (glargine or degludec), the patients were randomized to 26 weeks of double-blind URLi or lispro injected immediately prior to meals. The primary endpoint was change in hemoglobin A1c (HbA1c) from baseline to week 26 between URLi and lispro. The multiplicity-adjusted objectives were 1-and 2-h postprandial glucose (PPG) excursions after a test meal and change in HbA1c from baseline to week 26 in the URLi and lispro groups. Results: Results were obtained from prespecified exploratory analyses of 26-week data in Japanese patients randomized to receive URLi (n = 47) or lispro (n = 46). Mean baseline HbA1c levels significantly improved during the lead-in period to a baseline value of 7.50% and 7.60% in patients subsequently randomized to the URLi and lispro treatment groups, respectively. At week 26, the least squares mean (LSM) difference in HbAc1 between the URLi and lispro groups was 0.13% (95% confidence interval [CI]-0.12 to 0.39) (1.4 mmol/mol, 95% CI-1.3 to 4.2). Although there were no significant differences in PPG excursions at any time-point, numerically smaller PPG excursions were consistently observed from 30 min to 3 h during the mixed-meal tolerance test in patients on URLi compared to those on lispro. LSM differences in PPG excursions at week 26 were-10.5 mg/dL (95% CI-32.7 to 11.7) (-0.58 mmol/L, 95% CI-1.82 to 0.65) at 1 h and-14.9 mg/dL (95% CI-40.3 to 10.5) (-0.83 mmol/L, 95% CI-2.24 to 0.58) at 2 h. There were no significant differences between treatments in rates of severe/overall hypoglycemia or incidence of treatment-emergent adverse events. Conclusions: URLi administered as prandial insulin in combination with basal insulin provides effective glycemic control when administered immediately before a meal in Japanese patients with T2DM. URLi was well tolerated in this population.