Trelagliptin is the first once-weekly dipeptidyl peptidase-4(DPP-4) inhibitor in the world. Trelagliptin inhibits DPP-4 activity with lower drug concentration compared with other once- (or twice-) daily DPP-4 inhibitors in in vitro study. More than 70 % of DPP-4 activity is inhibited even 1 week after administration of trelagliptin administration in human study. 24-week trelagliptin monotherapy improved HbA1c(-0.33%) and fasting plasma glucose levels in Japanese patients with type 2 diabetes. Trelagliptin did not affect body weight and frequency of hypoglycemic events in this study. 52-week monotherapy and add-on therapy of trelagliptin also improved HbA1c levels without body weight gain and severe hypoglycemia. Therefore, trelagliptin has high efficacy and safety on glucose control in Japanese patients with type 2 diabetes.