The purpose of this study is to evaluate the safety and efficacy of a range of doses of SK-0403 in subjects with type 2 diabetes that are not adequately controlled on metformin alone.

Inclusion Criteria:

• Male and female subjects with type 2 diabetes between 18 and 75 years of age, inclusive
• Screening HbA1c between 7.0% to 10.0% for metformin stable subjects, 6.5% to 9.0% for subjects on metformin and 1 other antidiabetic agent (excluding thiazolidinediones, insulin, or incretin therapies [DPP-4 inhibitors and GLP-1 analogues]), or 7.5% to 11.0% for subjects on no antidiabetic medication or, if taking metformin, not on a stable dose of 1500 mg/day or maximum tolerated dose.
• No antidiabetic medication other than metformin for 3 months prior to randomization.
• Fasting plasma glucose less than 270 mg/dL (15 mmol/L) at screening.
• Body mass index between 20 kg/m2 and 45 kg/m2 inclusive at screening.

Exclusion Criteria:

• History of type 1 diabetes.
• Received treatment with insulin within 30 days of the screening visit or for more than 1 week within 3 months of the screening visit.
• Use of 3 or more oral antidiabetic medications at the time of the screening visit.