Compare the Effect of DPP-IV Inhibitor or TZD on Glycemic Variability and Oxidative Stress in Patient With 2 Diabetes

Inclusion Criteria: * Male or female with age 18-80 years * Type 2 diabetes mellitus * On stable dose of metformin (more than 1000mg) for at least 1 month * HbA1c 7\~10% * Subjects on statins, ACE inhibitors, ARBs and antioxidants will be allowed as long as they are on stable doses of these compounds and the dosage is not changed during the course of study * BP under control - no change required to BP medications * Agreement to maintain prior diet \& exercise Exclusion Criteria: * Type 1 DM or Any kind of secondary DM * Pregnant or lactating women. * Treatment with sulfonylurea, α-glucosidase inhibitor, glinide, GLP-1 analogues, DPP-IV inhibitors or insulin therapy within 1 month prior to informed consent. * Treatment with rosiglitazone or pioglitazone within 3 months prior to informed consent. * HbA1c \<7% or \>10% * Uncontrolled hypertension ( BP \> 160/100 mmHg) * Congestive heart failure (NYHA class I to IV).