Abstract: Objective; The study was performed to estimate insulin sensitivity of rats by the improved minimal model technique and explore the effects of age and weight on insulin sensitivity. Methods: We used the frequently sampled intravenous glucose tolerance test to collect blood samples of rats and measured the levels of glucose and insulin.Then we caculated S₁ and S_G by the minimal model software programmed by the Sun Yat-sen University of medical Sciences. Results: The SI of aged group is significantly lower than the young group.Weight negatively related to the insulin sensitivity. Conclusion: It is feasible to estimate insulin sensitivity by the improved minimal model technique in rats, Age and weight negatively related to the insulin sensitivity.