Abstract Aim To compare the efficacy and safety of acarbose plus metformin fixed-dose combination (FDC) versus acarbose monotherapy for type 2 diabetes (T2D). Methods Eligible T2D patients undergoing treatment with diet control only or oral antidiabetic medications were run-in on acarbose 50 mg thrice-daily for 4 weeks, then randomised either to continue this monotherapy, or to acarbose 50 mg plus metformin hydrochloride 500 mg FDC (acarbose/metformin FDC), each thrice-daily for 16 weeks. Results Acarbose/metformin FDC therapy significantly reduced HbA1c, fasting plasma glucose (FPG), and postprandial plasma glucose (PPG) from baseline (all p < 0.0001) with superior efficacy compared with acarbose monotherapy (between-group differences; HbA1c −1.35%; FPG −29.5 mg/dl; PPG −41.6 mg/dl; all p < 0.0001). Proportionally more patients treated with acarbose/metformin FDC achieved HbA1c <7.0% (47.8% vs. 10.7%, p < 0.0001). Both treatments reduced bodyweight ( p < 0.0001), with a significant between-group difference (−0.6 kg, p < 0.01) favouring acarbose/metformin FDC. Hypoglycaemia was not reported with either treatment, and the incidence of other adverse events did not differ significantly between the groups. Conclusions Compared with acarbose monotherapy, acarbose/metformin FDC has superior antihyperglycaemic efficacy, brings proportionally more T2D patients to HbA1c goal, and further reduces bodyweight. Acarbose/metformin FDC is well-tolerated without significant risk of hypoglycaemia and is a potentially advantageous therapy for T2D.