The purpose of this study was to investigate the relationship among plasma leptin, lipid profiles, insulin levels, and percentage of body fat of 72 schoolchildren from Obese Clinic Center in Seoul. The subjects divided into two groups: 39 obesity children [obesity index greater than $20\%$] who did not have a discernable medical cause of their obesity and 33 children with a obesity index less than $20\%$. The mean age, height, and obesity index of the subjects were 10.4 years, 144.0 cm, and $21.3\%$, respectively. The mean glucose and insulin levels of the obese children were 80.5 mg/dl and $13.3;{mu}IU/mL$ and those of the non obese children were 82.0 mg/dl and $4.2;{mu}IU/mL$, respectively. Obese children had significantly (p<0.05) higher level of total cholesterol, triglyceride, VLDL-cholesterol, LDL-cholesterol, and insulin concentration than non-obese children. However obese children had a lower level of HDL-cholesterol than non-obese children. Plasma leptin level were also positively correlated with BMI (p<0.000l), body fat (p<0.0001), tricep skinfold thickness (p<0.0001), mid arm circumference (p<0.0001), and waist hip ratio (p<0.0001). Plasma leptin showed a significantly positive correlation with insulin (p<0.0001), total cholesterol (p<0.0001), LDL-cholesterol (p<0.0001), and triglyceride (p<0.0001) levels, however, it was negatively correlated with HDL-cholesterol (p<0.0001) levels. In conclusion, the concentration of leptin in the blood is significantly correlated with the amount of body fat, BMI, plasma insulin, and plasma lipid profiles.