Abstract: The serum leptin level in 43 hyperthyroidism patients, 9 hypothyroidism patients, 21 normal controls are determined by radioimmunoassay(RIA ). The leptin level of different status of thyroid function in female is obviously higher than in male(P<0.05 ); the leptin average level of normal controls is lower than hyperthyroidism and hypothyroidism. Except there is no obvious differences (P>0.05) between male hyperthyroidism and normal controls, there is obvious differences between male with female hypothyroidism, female hyperthyroidism with normal controls (P<0.05). The results indicate that the serum leptin level is changed with the change of thyroid function at the same time.