Background: Dapagliflozin, a highly selective sodium-glucose cotransporter 2 inhibitor, reduces hyperglycemia, body weight, and blood pressure in patients with type 2 diabetes (T2D). Methods: This randomized double-blind placebo-controlled parallel-group 24-week study assessed the efficacy, safety, and tolerability of dapagliflozin added to metformin in Asian patients with inadequately controlled T2D (HbA1c 7.5%-10.5%). Patients were randomized to receive placebo (n = 145) or dapagliflozin 5 (n = 147) or 10 mg (n = 152). Results: Most participants were Chinese (86.0%), with a mean age of 53.8 years and mean T2D duration of 4.9 years; 92.1% completed the study. Adjusted mean HbA1c changes from baseline at Week 24 (primary endpoint) were -0.23%, -0.82%, and -0.85% in the placebo, dapagliflozin 5 and 10 mg groups, respectively, resulting in dapagliflozin 5 and 10 mg versus placebo differences of -0.59% and -0.62%, respectively (both P < 0.0001). Dapagliflozin 5 and 10 mg differences versus placebo were, respectively: -1.2 and -1.5 mmol/L for fasting plasma glucose; -1.1 and -1.8 kg for weight; and -2.3 and -2.7 mmol/L for 2-h postprandial glucose (all P < 0.0001). In the placebo, dapagliflozin 5 and 10 mg groups, respectively: adverse events (AEs) occurred in 52.4%, 52.4%, and 55.3% of patients; serious AEs occurred in 4.1%, 2.0%, and 2.0%; urinary tract infections occurred in 4.8%, 4.1%, and 6.6%; and genital infections occurred in 0%, 2.0%, and 1.3%. No AEs of pyelonephritis or renal failure occurred. Conclusions: Dapagliflozin 5 or 10 mg as add-on tometformin was well tolerated in Asian patients with T2D and significantly improved glycemic control with the additional benefit of weight reduction.