This is a phase 4, single center, randomized, open-labeled study. The primary objective of the study is to compare effect of gemigliptin and acarbose on endothelial function.

Subjects are randomized to gemigliptin or acarbose group and maintained intial treatment for 4 weeks.

Inclusion Criteria:

• age: 20-80yrs
• patients with type 2 diabetes (duration of diabetes >=3 months)
• HbA1c :>7.0 and <=9.0% on metformin monotherapy
• no changes on medications during recent 3 months.

Exclusion Criteria:

• patients with type 1 diabetes
• history of medications including α-glucosidase inhibitor, glinide, GLP-1 analogue, other DPP-4 Inhibitors, or insulin during recent 3 months.
• history of acute diabetic complication, acute coronary events, or coronary bypass surgery/interventions during recent 6 months.
• patients with congestive heart failure (NYHA II~IV) or clinically significant ventricular arrhythmia
• serum ALT or AST> 2.5 x upper normal range
• serum direct bilirubin > 1.3 x upper normal range
• serum creatinine > (men) 1.5 mg/dL, (women)>1.4 mg/dL
• smoker
• pregnant women, or breast-feeding women
• medication with acetylsalicylic acid or vitamin K antagonist