Type 2 Diabetes Mellitus (T2DM) is characterized by high blood glucose in the context of insulin resistance and relative insulin deficiency. Diabetes is often initially managed by increasing exercise and dietary modification. As the condition progresses, medications may be needed such as oral sulfonylurea or others. Recently, dipeptidyl peptidase 4 (DPP- 4) Inhibitor is new drug which can control blood glucose by increasing the active levels of incretin hormone in the body. However, researches have been carried out for mostly Caucasian and Japanese, not for Koreans at all. Therefore, this study was to evaluate the efficacy and safety of DPP-4 inhibitor (Sitagliptin, Vildagliptin) in patients with T2DM in Koreans. This study was carried out retrospectively with reviewing of medical records from the 141 patients who received sitagliptin or vildagliptin over 24 week periods from January 2009, to December 2009. Information including demographics, concomitant medication, disease duration, and exercise was evaluated. $HbA_{1c}$, random blood glucose, post prandial 2 hour glucose, blood pressure, AST, ALT, serum creatinine, total cholesterol, triglyceride levels were also collected at baseline and endpoint (at 24 weeks). In each post-treatment group, $HbA_{1c}$, random blood glucose and post prandial 2 hour glucose levels were decreased significantly from baseline in the sitagliptin group (-0.82%, -28.76 mg/dl, -46.65 mg/dl) and vildagliptin group(-1.22%, -27.96 mg/dl, -67.2 mg/dl). Greater $HbA_{1c}$ mean reductions from baseline to 24 weeks were seen in patients with higher baseline values (>7.0%), with shorter disease durations (${leq}1$ year) compared with those with lower baseline values (<7.0%), with longer disease durations (>1 year) in both sitagliptin and vildagliptin groups. The incidences of hypoglycemia, headache and upper respiratory infection were 0%, 8.7%, 5.8% in sitagliptin group and 2.8%, 8.3%, 6.9% in vildagliptin group. In conclusion, our results showed DPP-4 inhibitor provided similar efficacy compared with sulfonylurea after 24 weeks of treatment and were safer than sulfonylurea in hypoglycemia for Korean T2DM. Also vildagliptin was associated with significant improvement in $HbA_{1c}$ reduction in Korean patient with subgroup (body mass index<25 $kg/m^2$, metformin dose${geq}$1000 mg, p<0.05) compared to sitagliptin. Therefore, even though DPP-4 inhibitor use for Korean needs to be studied more consistently in the future, DPP-4 inhibitor is a safe and effective drug for Korean T2DM based on our result.