This study evaluates the efficacy and safety and population PK of HMS5552 as monotherapy in adult type 2 diabetic subjects, there will be 2 groups in the first 24 weeks, one group will receive HMS5552 , while the other group will receive placebo ; after 24 weeks, all subjects will receive HMS5552 for 28 weeks.

This study is a phase III study in subjects with T2DM. As designed, the study will start with a 4-week, single-blind, placebo run-in period based on diet and exercise interventions for screening eligible subjects. The eligible subjects are randomly assigned to HMS5552 75mg BID group or placebo BID group with ratio 2:1 to receive a 24-week double-blind treatment. Then all subjects receive 28-week open-label treatment of HMS5552 75mg BID . After 52-week treatment, all investigational drugs should be discontinued, followed by 1 week for safety evaluation.

Inclusion Criteria:

1. Male or female, aged 18~75 years old
2. naive T2DM 3.7.5% ≤ HbA1c ≤ 11.0% at screening 4.18.5 kg/m2 < BMI < 35.0 kg/m2 at screening;

Exclusion Criteria:

1. T1DM
2. Fasting C-peptide <1.0 ng/ml (0.33 nmol/L) at screening
3. Medical history of severe hypoglycemia, diabetic ketoacidosis, diabetes lactic acidosis or hyperosmotic nonketotic diabetic coma, severe cardio-cerebrovascular,unstable or rapidly progressive kidney disease, active liver diseases,diagnosed mental disease,etc