Mazdutide is a once-weekly glucagon and glucagon-like peptide-1 receptor dual agonist developed for the treatment of type 2 diabetes (T2D) 1. This study assessed the efficacy and safety of mazdutide versus dulaglutide in participants with T2D on background oral anti-diabetic drugs. In this randomised phase 3 study, 731 participants with T2D were randomised 1:1:1 to receive mazdutide 4 mg, mazdutide 6 mg or dulaglutide 1.5 mg for 28 weeks. Both mazdutide doses demonstrated non-inferiority and superiority to dulaglutide 1.5 mg in mean change in HbA 1c from baseline to week 28, with the least squares (LS) mean treatment difference of −0.24% (p=0.0032) for mazdutide 4 mg and −0.30% (p=0.0003) for mazdutide 6 mg vs dulaglutide 1.5 mg. Significantly greater weight reductions were achieved with mazdutide versus dulaglutide, with LS mean treatment difference of −3.78% for mazdutide 4 mg and −5.76% for mazdutide 6 mg vs dulaglutide (both p<0.0001). Moreover, significantly more participants with mazdutide achieved the composite endpoint of HbA 1c <7.0% with ≥5% weight reduction vs dulaglutide 1.5 mg at week 28 (both p<0.0001). The most common treatment-emergent adverse events were diarrhoea, nausea, and vomiting. Our findings showed that 28-week treatment with mazdutide (4 mg and 6 mg) provided superior reductions in HbA 1c and body weight compared with dulaglutide 1.5 mg in Chinese participants with T2D. Mazdutide was generally safe, with a higher incidence of gastrointestinal adverse events than dulaglutide.