Abstract: Objective The aim of this study was to evaluate effect of chitosan on rat body weight,concentration of plasma leptin,serum testosterone and their relationships.Methods Five groups of rats were respectively given access to base diet,high fat diet and high fat diet containing different doses of chitosan for 7th weeks.All rats were weighed once a week.By the end of 7th week,the animals were sacificed and their blood samples were taken,the concentration of plasma leptin and serum testostero ne were determined by RIAK it method.Results Chitosan prevented the increase of body weight induced by a higth-fat diet and lowered serum testosterone concentration.Based on analysis on the changes of body weight and plasma leptin level,it is inferred that chitosan could give rise to the augment of leptin in plasma.Conclusion The concentration of serum testoster one reduced by chitosan could stiumlate the secretion of leptin,which could be in part responsible for the inhibiting the increase of body weight induced by high-fat diet.