Objective To compare the efficacy and safety of combining sitagliptinin to therapy type 2 diabetes mellitus (T2DM) of elderly patients with inadequate glycemic controlled by metformin monotherapy.Methods A total of 52 T2DM elderly patients [30 males and 22 females, at an age of (68.0±8.0) years, ranging from 65 to 78] with inadequate glycemic controled by metformin monotherapy admitted in our department from May 2015 to September 2016 were recruited in this study. They were randomly divided into sitagliptin group and acarbose group, with 26 ones in each. Besides oral administration of 500 mg metformin (3 times per day), the former group was treated with 100 mg sitagliptin (once per day), and the latter with 50 mg acarbose (3 times per day), for 12 consecutive weeks.Then fasting plasma glucose(FBG), 2-hour postprandial glucose(2hPG), hemoglobin A1c(HbA1c) and body mass index (BMI)were measured in the 2 groups. The incidences of hypoglycemia and gastrointestinal adverse reactions were observed. ResultsNo difference was seen in the FBG, 2hPG and HbA1c in the 2 groups before treatment (P>0.05). After the treatment, the above 3 indicators were significantly reduced (P<0.05). The declines of 2hPG and HbA1c were more obvious in the sitagliptin group than acarbose group (P<0.05). No hypoglycemia was observed during treatment. In acarbose group, 4 cases complained of abdominal distention and increased flatus passage. No statistical difference was observed in gastrointestinal adverse reactions between two groups (P>0.05). Conclusion Combined of sitagliptin with metformin shows significant efficacy and safety in treatment of T2DM elderly patients.