OBJECTIVE To investigate the relationship between fasting serum levels of leptin, glucose, insulin resistance, lipids in simple obese children. METHODS Fasting serum levels of leptin and insulin (Fins) were measured by RIA in 42 obese and 42 normally-weighted children matched on age, sex and height, and their total cholesterol (TC), triglyceride (TG), high density lipoprotein-cholesterol (HDL-C) were analyzed with enzymatic methods. HOMA-IR and LDL-C were calculated. RESULTS Serum level of leptin was (2.74 - 45.12) micro g/L and (0.53 - 10.18) micro g/L in obese and normally-weighted children, respectively, with an average level of leptin (log) significantly higher in obese group than that in control group (P < 0.001). Serum level of leptin was positively correlated with BMI, WHR and percentage of body fat. Of obese children, 83% were leptin resistant. Serum levels of TC, TG, LDL-C and insulin were significantly higher in obese leptin-resistant group than those in normally-weighted control group, but no significant difference in them between obese leptin-sensitive group and its normally-weighted control group was observed. Significantly higher serum levels of TG and lower HDL-C were observed in obese leptin-resistant group, as compared with those in obese leptin-sensitive group. CONCLUSIONS A big difference in serum level of leptin between obese and normally-weighted children was found, suggesting most obese children were resistant to endogenous leptin. Leptin resistance correlated significantly with the risk of metabolic syndrome and cardiovascular disease, indicating serum level of leptin could be used as an indicator in screening obese children at high risk.