Abstract: Objective To analyze the relationship between serum leptin concentration and simple obesity of teenagers.Methods The serum leptin concentration was measured by RIA in 998 teenagers in Lanzhou.Results There was a positive correlation between serum leptin concentration and BMI(r=0.310,P<0.01).In both girls over 10 years old and boys over 13 years old,the serum leptin concentrations of the obese groups were obviously higher than that of the normal weight and thinner(P<0.05).There was no correlation between the sex and the serum leptin concentration(r=0.030,P=0.374).But for subjects over 13 years old the sex differences had statistical significance(P<0.05).The serum leptin concentration and the age presented a negative correlation(r=-0.120,P=0.004).Conclusion The leptin and the obesity degree presented a positive correlation.There was leptin resistance among the obese teenagers.Serum leptin concentration could be regarded as an important evaluation index of teenagers' simple obesity.