Aims/Introduction: The aim of the present study was to evaluate the safety and efficacy of luseogliflozin added to liraglutide monotherapy in Japanese individuals with type 2 diabetes. Materials and Methods: This 52-week, multicenter, open-label, single-arm clinical study enrolled Japanese patients who had inadequate glycemic control with diet/exercise and liraglutide monotherapy. Major efficacy end-points included the changes from baseline in glycated hemoglobin, fasting plasma glucose and bodyweight. Body composition was also assessed in individuals who had access to bioelectrical impedance analysis. Safety assessments included adverse events, clinical laboratory tests, vital signs and 12-lead electrocardiograms. Results: Of 76 patients who received luseogliflozin, 62 completed the study. The changes from baseline in glycated hemoglobin, fasting plasma glucose, and bodyweight (mean ± SE) were −0.68 ± 0.10%, −32.1 ± 3.6 mg/dL and −2.71 ± 0.24 kg at week 52, respectively (all, P &lt
0.001 vs baseline). Luseogliflozin was associated with greater reductions in fat mass than lean mass at all measuring points (n = 22): fat vs lean mass changes (mean ± SE) at week 52 were −2.49 ± 0.45 kg (P &lt
0.001 vs baseline) and −0.44 ± 0.26 kg (P = 0.107 vs baseline), respectively. Insulin secretion and Matsuda Index were also improved at weeks 12 and 52 compared with baseline. Adverse events and adverse drug reactions occurred in 65.8 and 27.6% of patients, respectively. The overall safety profile, including frequency of hypoglycemia, was found to be consistent with those of previous studies and there were no new safety concerns. Conclusions: Luseogliflozin added to liraglutide was well tolerated, and improved glycemic control with bodyweight and fat mass reductions in Japanese type 2 diabetes patients.