This study is to examine the change of fasting insulin, glucose, insulin sensitivity and related traits in response to the six month treatment of omega-3 fatty acids, including fish oil and flaxseed oil, in Chinese type 2 diabetic patients. Corn oil, rich in omega-6 fatty acids, will be selected as a controlled oil. The investigators hypothesize that omega-3 fatty acids could improve insulin sensitivity and glucose metabolism in Chinese type 2 diabetic patients.

The insulin resistance will be estimated by a homeostatic model assessment model of insulin resistance (HOMA-IR)

Inclusion Criteria:

1. Fasting glucose > 7.0 or have diabetes medication;
2. Male, 35-80 years; female, postmenopausal to 80 years;
3. Agree to participant in the trial.

Exclusion Criteria:

1. Deny to sign the informed consent;
2. type 1 diabetes;
3. Family history of hypertriglyceridemia or fasting triglyceride>4.56 mmol/L;
4. Have severe liver disease, kidney disease or cancer;
5. Participating in the other clinical trial within 30 days;
6. Other diseases or conditions, for which the doctor of the patients do not agree his or her participating.