Canagliflozin is a sodium-glucose cotransporter 2 inhibitor under development for the treatment of type 2 diabetes. Our aim was to examine its efficacy and safety as monotherapy or in combination with commonly used oral antihyperglycemic drugs in Japanese patients with type 2 diabetes. Patients on diet/exercise alone or diet/exercise plus an oral antihyperglycemic drug (sulfonylurea, glinide, α-glucosidase inhibitor, biguanide, thiazolidinedione or dipeptidyl peptidase-4 inhibitor) were randomized to either 100 or 200 mg canagliflozin while continuing prior therapy. Patients were treated for 52 weeks in an open-label manner. Canagliflozin significantly reduced hemoglobin A1c, fasting plasma glucose and bodyweight in all the study groups. Improvements were apparent by 4 weeks of treatment, and were maintained for 52 weeks. The reduction in hemoglobin A1c ranged from -0.80 to -1.06%, and from -0.93 to -1.26% in the 100 and 200 mg canagliflozin groups, respectively. Drug-related adverse events occurred in approximately one-third of patients, and included hypoglycemia/asymptomatic hypoglycemia and pollakiuria. Hypoglycemia/asymptomatic hypoglycemia was most common in patients treated with a sulfonylurea. Most adverse events were classified as mild or moderate in severity. The results of the present study confirmed that treatment with canagliflozin resulted in significant reductions in glycemic control and bodyweight that were maintained for 52 weeks of treatment irrespective of whether it was administered as monotherapy or in combination with another oral antihyperglycemic drug. Canagliflozin was well tolerated, with a low incidence of drug-related adverse events. This trial was registered with ClinicalTrials.gov (no. NCT01387737).