Abstract: Objective To compare islet β-cell function in type 2 diabetic (T2DM) patients with different glycosylated hemoglobin (HbA1c) levels and diabetes durations. MethodsWe examined body parameters, biochemical profiles and islet autoantibodies in a total of 803 T2DM patients admitted in the Department of Endocrinology of the First Affiliated Hospital of Nanjing Medical University between December, 2014 and April, 2016. The patientswere stratified by HbA1c level and disease course and underwent steamed bun test to evaluate islet β-cell function and insulin resistance. Results Linear correlation analysis showed that in T2DM patients, HbA1c level was negatively correlated with HOMA2-IR, HOMA2-%β, DI30 and DI180 (P=0.000), and disease course was negatively correlated with HOMA2-IR, HOMA2-% β, and DI180 (P<0.05). The patients with different HbA1c levels showed significantly different HOMA2-IR, HOMA2-%β, DI30 and DI180 (P=0.000); HOMA2-%β, DI30 and DI180 were significantly higher in patients with HbA1c levels <7.8%, and HOMA2-% β was significantly decreased in patients with HbA1c levels above 9.8%. The patients with different disease courses also had significant differences in HOMA2-IR, HOMA2-%β, DI30, and DI180 (P=0.000), and as the disease course extended, DI30 and DI180 tended to decrease progressively. Multivariate linear regression analysis showed that HbA1c, diabetes duration, and body mass index (BMI) were all independent factors affecting islet β- cell function in T2DM patients. Conclusion The secretion function of islet β cells decreases progressively with the increase ofHbA1c level or disease course in T2DMpatients, but the disease course does not appear to have an effect as strong as that ofHbA1c level on islet β cell function.