Abstract: Objective To study on relationship between insulin resistance and leptin resistance in obese-developing rats cause-effect relationship between them.Methods Twenty rats were separated to two groups by random:normal group fed normal diet and obese-developing group fed high fat diet.The animals were fed five weeks.The tail blood was collected at each weekend,which was used to measured blood sug ar,insulin and leptin.Results Weight,levels of blood sugar,insulin and leptin in obese-developing group were higher than normal group.Leptin resistance appeared at the second week and the insulin resistance appeared at the third week.The timing of leptin resistance appearance was earlier than that of insulin resistance appearance in obese-developing rats.It suggested that leptin resistance was the cause of insulin resistance.Conclusion Obesity was the impontant risk factor.