After a screening, a 2-week, single-blind placebo run-in, 174 patients will be randomized in a 1 : 1 ratio to the addition of either once-daily Gemigliptin 50 mg or placebo to ongoing stable doses of glimepiride in combination with metformin for 24 weeks.

Subjects will visit the center on Week 6, 12, 18 and 24 during the entire 24-week treatment period. Total study duration will be approximately 26weeks and the subjects will be to practice exercise/diet control together.

Inclusion Criteria:

1. Patients with Type 2 Diabetes Mellitus
2. Adults aged ≥ 19 years old
3. Patients with HbA1c 7%~11% at Visit 1