Abstract: Objective: To observe the changes of insulin sensitivity in high-fat-induced obese rats and the effects of glucocorticoid.Methods: The adult rats were fed with high fat food for 80 days and the obese ones were selected.The fasting blood glucose,the fasting insulin and the degree of insulin resistance of the obese rats were compared with that of the normal ones.Both the obese rats(n=40) and the normal rats(n=38) were intraperitoneally injected normal saline and different doses of hydrocortisone succinate,and the serum levels of fasting blood glucose,fasting insulin and the degree of insulin resistance were observed.Results: The obeses rats had higher serum levels of fasting blood glucose,fasting insulin and insulin resistance than the normal ones(P<0.001).Compared with the normal saline group,the serum levels of fasting blood glucose,fasting insulin and the degree of insulin resistance were increased in the hydrocortisone succinate group(P<0.01).Conclusions: Obesity may cause hyperinsulinemia and insulin resistance,and glucocorticoid can induce insulin resistance.