We analyzed the effects of 100 mg/day sitagliptin and a switch to mitiglinide calcium hydrate/voglibose compound tablets (MIT/VOG) in patients with type 2 diabetes mellitus (T2DM) treated with 50 mg/day sitagliptin. Five patients with T2DM treated with 50 mg/day sitagliptin and hemoglobin A1c (HbA1c) of ≥6.5% were switched to MIT/VOG, or the dose of sitagliptin was increased to 100 mg/day. The effects of the changes in therapy were compared in a crossover fashion by continuous glucose monitoring. The primary endpoint was mean amplitude of glycemic excursions (MAGE), and the secondary end points were 24-hour mean blood glucose level and mean blood glucose level from 0:00 a.m. to 7:00 a.m. and from 7:00 a.m. to 0:00 a.m., percentage of time with blood glucose level of ≥200 mg/dl and <70 mg/dl, maximum and minimum blood glucose levels, and increases in postprandial blood glucose levels. MAGE was significantly lower with MIT/VOG (P = 0.016), whereas mean blood glucose levels were lower between 0:00 a.m. and 7:00 a.m. with 100 mg/day sitagliptin. The percentage of time with blood glucose level ≥200 mg/dl was significantly shorter with MIT/VOG (P = 0.041). The maximum blood glucose level was significantly lower with MIT/VOG (P = 0.043), and the minimum was significantly lower with 100 mg/day sitagliptin (P = 0.043). Blood glucose levels after dinner and mean increases in postprandial blood glucose levels were significantly lower with MIT/VOG (P = 0.090 and P = 0.045 respectively). In patients with T2DM, treatment with MIT/VOG improves MAGE and postprandial hyperglycemia and 100 mg/day sitagliptin lowers early morning glucose levels. This trial was registered with the University Hospital Medical Information Network (UMIN) (No. UMIN R000008274).