In this present study, the modified Oral Minimal Model (OMM), with secretion of insulin from pancreas was assumed that the insulin decay rate was not always a first-orderly process in the Oral Glucose Tolerance Test (OGTT), had been developed to study Normal Glucose Tolerance (NGT), Impaired Glucose Tolerance (IGT or pre-diabetes) and type 2 Diabetes Mellitus (T2DM) subjects. The modified OMM model was used to assess physiological functions which were insulin sensitivity (S I ) and glucose effectiveness (S G ) from the OGTT data. The results of the modified OMM model fit to the measured glucose and insulin concentration-time profiles in the OGTT process of the subjects. The single-step fitting process to optimize the real pAarameters of the S I and S G index from the experimental data using the modified OMM. Our results showed that all NGT subjects had higher the S I and S G index than all IGT and T2DM subjects following the OGTT process. Basal and large peak glucose were lower in all NGT subjects than in all IGT and T2DM subjects. Insulin extraction was lower in all subjects with T2DM but was almost similar for the NGT and IGT subjects. The averaged correlation between measured and this present model, commonly called R 2 value, showed that these four cases were 0.96 which indicated good agreement.