Obesity is the disorder of the mechanisms in balancing food intake and energy expenditure. It leads to several diseases such as type Ⅱ diabetes,hypertension,hyperlipidaemia and cancers. The positional cloning of the obese gene provides an important approach to the research of the mechanisms of obesity. Leptin,the product of obese gene,acts on the hypothalamus, controlling metabolism, energy expenditure and reproductive system. Research data showed that the recombinant leptin normalized the metabolism and body weight of the obese gene defficiency mice and the neuropeptide Y defficiency mice,corrected the sterility of the obese gene defficiency mice. Further researches on the mechanisms of the obese gene and development of the drugs according to different kinds of defficiency can make it possible to the treatment of obesity.