Abstract: Leptin is a hormone synthesized and secreted by lipid cells.It is a product encoded and expressed by the obese gene. Administration of recombinant leptin decreases food intake,increases energy expenditure and promotes weight loss. Most studies indicate that leptin is a main regulating factor of catabolism and anabolism of adipose tissue. The circulating leptin level is a sensitive index which indicates the confusion of the rate of lipid metabolism such as hyperlipemia, lipoliver and so on.The human leptin radioimmunoassay has been developed to quantitate human leptin in plasma or serum, and to further investigate the relationship between serum leptin concentration and body fat, gender,age,sexual hormones, endocrine of insulin, etc. Especially, serum leptin concentrations are correlated with body-mass-index (BMI),suggesting that most obese persons are resistant to leptin; Those who are relatively deficient of leptin may become the good candidates of leptin treatment in the future.The discovery and application of leptin make the study of obesity,non-insulin dependent diabetes and other correlation diseases enter a new stage.