Type 2 diabetes mellitus (T2DM) is a heterogeneous disorder characterized by defects in insulin secretion and action and obesity plays an important role in the deterioration of glucose metabolism. In the present study we evaluated the degree of insulin resistance and first-phase insulin secretion of beta-cell in obese subjects with normal glucose tolerance (NGT), impaired glucose tolerance (IGT), and T2DM in Chinese. A total of 220 subjects underwent standard 75 g oral glucose tolerance test (OGTT) and insulin-modified frequently sampled intravenous glucose tolerance test (FSIGT). Insulin sensitivity index (S I) was assessed by the reduced sample number (n = 12) of Bergman's minimal model method with FSIGT. Insulin secretion capacities were determined by the insulinogenic index (I 30 min - I 0 min)/(G 30 min - G 0 min) in OGTT and the acute insulin response to glucose (AIR) in FSIGT. The disposition index (DI), the product of AIR and S I was used to determine whether AIR was adequate to compensate for insulin resistance. The S I in healthy lean control group was significantly higher than that in NGT, IGT, and T2DM group, but there was no significant difference among NGT, IGT, and T2DM group. The AIR in NGT group was significantly greater than that in control group, but then it was progressively decreased in IGT and T2DM group. The value of DI in control group was significantly higher than that in those three abnormal groups, and was decreased from NGT to IGT and T2DM group with significant difference. It indicates that obese subjects with different glucose tolerances have a similar degree of insulin resistance but differ in insulin secretion in Chinese Han population.