Objective This phase 3 confirmatory diabetes mellitus treatment study compared the safety and efficacy of Rapilin and NovoRapid insulin asparts in combination with metformin. Methods This 24-week, open-label, randomized, active-controlled, noninferiority phase 3 confirmatory study conducted across centers in China aimed to enroll patients with type 2 diabetes mellitus and blood sugar glucose inadequately controlled by oral antidiabetic drugs. Randomized patients received subcutaneous mealtime Rapilin or NovoRapid (3:1) injections, with metformin. The primary objectives were to demonstrate noninferiority (margin of 0.4%) in HbA1c change from baseline and compare safety profiles of Rapilin versus NovoRapid after 24 weeks. Secondary outcomes included 2-h postprandial plasma glucose (PPG), fasting plasma glucose (FPG), and patients achieving HbA1c Results 590 patients with type 2 diabetes mellitus were randomized to Rapilin (n = 441) and NovoRapid (n = 149) groups. After 24 weeks, the mean HbA1c change from baseline was -2.20% (Rapilin) and -2.32% (NovoRapid); the estimated treatment difference based on least-square means was 0.04% (95% CI: -0.17, 0.26), meeting the noninferiority criteria for Rapilin versus NovoRapid. Comparable improvements were reported for mean 2-hour PPG (6.14 and 6.29 mmol/L), FPG (2.02 and 1.70 mmol/L), and patients with HbA1c <7.0% (52.6% and 51.0%) and <= 6.5% (34.2% and 30.9%), in the Rapilin and NovoRapid groups, respectively, with no significant safety or immunogenicity outcome differences. Conclusions Rapilin demonstrated non-inferior glycemic control, and matching safety and immunogenicity to NovoRapid in patients with type 2 diabetes mellitus also receiving metformin over 24 weeks.