The primary objective of this study is to demonstrate whether mitiglinide administered in combination with metformin is more effective than metformin alone in patients with Type 2 diabetes mellitus (T2DM) whose blood sugar is not well controlled taking metformin alone. This is a 24 week study which measures improvement in blood sugar after of treatment.

This is a randomized, double-blind, placebo-controlled, parallel group study designed to evaluate the efficacy and safety of mitiglinide in combination with metformin in patients with T2DM who are less than adequately controlled on metformin alone. Patients who are receiving metformin alone for T2DM will be randomized equally into one of three treatment groups.

Inclusion Criteria:

• type 2 diabetes diagnosed for at least 6 months
• stable metformin usage for at least 4 months
• HbA1c 7.5% - 10.5% inclusive
• no severe diabetic complications

Exclusion Criteria:

• chronic insulin use
• use of oral diabetic agent within 12 weeks
• acute or chronic conditions, excluding diabetes, that could compromise end point evaluation