Aims To assess the efficacy and safety of twice-daily insulin degludec/insulin aspart (IDegAsp) versus biphasic insulin aspart 30 (BIAsp 30) twice daily, both +/- metformin, in Chinese adults (N = 543) with type 2 diabetes (T2D) inadequately controlled on premixed/self-mixed or basal insulin +/- metformin. Materials and methods We conducted a 26-week, phase III, open-label, treat-to-target, 2:1 randomized trial. Hierarchical testing was used with non-inferiority of glycated haemoglobin (HbA1c) change from baseline to week 26 as the primary endpoint and superiority for the confirmatory secondary endpoints which were as follows: change from baseline in fasting plasma glucose (FPG); nocturnal confirmed hypoglycaemic episodes (12:01-5:59 am, inclusive); total confirmed hypoglycaemic episodes (severe or plasma glucose <3.1 mmol/L with/without symptoms); body weight; and percentage of responders (HbA1c <53 mmol/mol [<7.0%]) without confirmed hypoglycaemic episodes. Results Non-inferiority for change from baseline to week 26 in HbA1c and superiority of IDegAsp twice daily versus BIAsp 30 twice daily for change in FPG, nocturnal confirmed and total confirmed hypoglycaemic episodes, was demonstrated. Estimated rates of nocturnal confirmed and total confirmed hypoglycaemic episodes were 47% and 43% lower, respectively, with IDegAsp twice daily versus BIAsp 30 twice daily. Superiority for change in body weight was not confirmed. Participants were more likely to reach the HbA1c goal of <53 mmol/mol (<7.0%) without confirmed hypoglycaemia with IDegAsp twice daily versus BIAsp 30 twice daily by trial end. No new safety signals were identified. Conclusions The efficacy and safety of IDegAsp in Chinese patients with T2D was demonstrated, confirming results from international trials.