The purpose of this study is to evaluate the efficacy and safety of 3 different doses of SHR3824 compared with placebo in patients with type 2 diabetes mellitus who are receiving treatment with metformin monotherapy (ie, treatment with a single drug) and have inadequate glycemic (blood sugar) control.

Inclusion Criteria:

• Patients must have a diagnosis of type 2 diabetes mellitus;
• Hemoglobin A1c levels >=7.5% and <=10.5%;
• Body mass index (BMI) 25 to 45 kg/m2;
• Patient either has been treated with metformin for more than 8 weeks with dose more than 1500mg/day.

Exclusion Criteria:

• Type I diabetes mellitus, diabetes mellitus resulting from pancreatic disorder, or secondary diabetes mellitus (acromegaly, Cushing's syndrome, etc.);
• Past or current history of severe diabetic complications (proliferative diabetic retinopathy, stage III or later stage overt nephropathy, diabetic ketoacidosis, or serious diabetic neuropathy);
• Systolic blood pressure of ≥160 mmHg or diastolic blood pressure of ≥100 mmHg on the start or end day of the run-in period;
• History of myocardial infarction, unstable angina, or cerebrovascular disorder within 6 months before the start of the run-in period;
• Past or current history of malignant tumor;
• Past or current history of drug hypersensitivity such as shock and anaphylactoid symptoms;
• Pregnant women, lactating mothers, or women of childbearing potential;
• Any condition that subjects are assessed to be ineligible by the investigator (sub investigator).