Abstract: Objective To investigate the levels of serum Leptin,Insulin and the correlation between them and the body mass index (BMI) in simple obesity of the preschool children. Methods We selected 56 cases of simple obesity of the preschool children in health physical examination as the obesity group,which were from three kindergarten of Yan'an from March to July 2015.At the same time,56 children with the same age,gender,similar height and normal body mass were selected as the control group.Then we determined and analysed serum Leptin and Insulin levels in two groups by radioimmunoassay. Results The level of serum Leptin and Insulin in the obesity group were significantly higher than those in the control group (P<0.01).However,there were not significantly difference of the Leptin and Insulin levels in two groups when compared between male and female (P>0.05).There were positive correlation between serum Leptin,Insulin levels and BMI in the obesity group (P<0.05).Serum Leptin and Insulin levels were higher in the older age group than those in the younger age group of obese children (P<0.05). Conclusion The level of serum Leptin and Insulin in simple obesity of the preschool children are significantly higher than those in healthy children.The results show that simple obese children have a resistance of Leptin and Insulin.Periodically determined the level of serum Leptin and Insulin in simple obese children has certain significance in the guiding of early intervention in simple obesity of the preschool children.