Study of the Durability of Glycemic Control With Nateglinide

Inclusion Criteria: * type 2 diabetes mellitus * age\>=18years * no anti hyperglycemic agent for 3 months or low-dose oral hypoglycemic therapy * metformin≤1g/day, acarbose≤300mg/day, voglibose≤0.9mg/day, nateglinide≤270mg/day, gliclazide≤80mg/day, glimepiride≤2mg/day, glibenclamide≤5mg/day (nateglinide or sulfonylurea \<6months) * 6.5% ≤ HbA1c ≤ 8.5% * patients on no anti hyperglycemic agent for 3 months : HbA1c at screening * patients on oral hypoglycemic therapy in 3months : HbA1c after wash-out Exclusion Criteria: * attending other clinical trials in 3months * type I diabetes mellitus * taking systemic steroid in 1month or requiring steroid therapy during clinical trial * acute myocardial infarction in 6months * alcoholics, pituitary or adrenal insufficiency, severe ketosis, diabetic ketoacidosis * severe liver disease or AST, ALT ≥ 2.5 x ULN * renal insufficiency (serum creatinine \> 2.0mg/dl) * other severe diabetic complication * drug hypersensitivity history to nateglinide or sulfonylurea * pregnant or plan to become pregnant during the clinical trial, lactation