Objective To investigate the changes of postprandial serum insulin and C-peptide concentration of type 2diabetes mellitus (T2DM) patients with different fasting blood glucose concentrations, and to study the islet function of them.Methods There were 492T2DM patients from January 2016to June 2017in our hospital were selected and divided into three groups according to different fasting plasma glucose (FPG) levels:group A, 7.0mmol/L≤FPG＜11.1mmol/L;group B, 11.1mmol/L≤FPG＜14.0mmol/L;group C, FPG≥14.0mmol/L.Meanwhile, 50healthy examinees were collected as the control group.A standard 75g OGTT were performed in 492T2DM patients and 50healthy controls, and 2mL of venous blood of them were collected at 0.5, 1.0, 2.0and 3.0h.The concentration of insulin and C-peptide at each point was measured by chemiluminescence method, and then compared with the control group.Results The concentration of insulin and C-peptide in T2DM patients were slightly higher than those in the control group, but there was no statistical significance (P＞0.05).The serum insulin and C-peptide post-meal in the A, B and C groups and control group increased, but the 1.0hpostprandial blood glucose of control group increased to a peak, and gradually returned to normal at 3.0h;the 2.0hpostprandial blood glucose of A, B and C groups increased to a peak, and decreased at 3.0h, but did not return to normal level.The concentrations of insulin and C-peptide in the A, B and C groups at 0.5, 1.0, and 2.0hpost-meal were significantly lower than those in the control group (P＜0.05).Conclusion The function of isletβcells in T2DM patients decreases with the increase of blood glucose.The determination of insulin and C-peptide can provide a scientific evidence for judging the severity of disease and guiding treatment.