Abstract： ObjectiveTo explore discuss the role of proins ul in in the onset of T2DM by observing the serum proinsulin levels of fasting and post-intravenous glucose tolerance in the subjects with varying degrees of ins ulin resistance and β cell function.MethodsThe proinsulin l evels were measured by RIA in 76 subjects with simple obesity, impaired glucose tolerance or T2DM. Correlation analysis were used to show the relationships amon g proinsulin, obesity, β cell function index and insulin sensitive index etc.ResultsFasting proinsulin level was much higher in simple obes e, IGT and T2DM groups than in normal control, while no difference could be foun d among the groups of simple obese, IGT and T2DM. The proinsulin serum level was significantly correlated with BMI, WHR, fasting and postprandial glucose level, fasting insulin and insulin sensitivity index. The profile of the proinsulin se cretion curve was almost the same in IVGTT for the four groups, except the delay ing of peaks in groups of simple obese, impaired glucose tolerance and T2DM.Conclusion Fasting proinsulin level is most positively related wi th the glucose levels (fasting or postprandial) and insulin resistance. The proi nsulin is increased in simple obese, IGT and T2DM. To some extent, hyperinsulin emia might be modified by hyperproinsulinemia in simple obese subjects, which mi ght indicate that β cell dysfunction could exist in the simple obese stage befo re the onset of T2DM.