To study the changing regularity of leptin during puberty in girls and the relationship of leptin, estradiol and testosterone each other, serum levels of leptin, estradiol(E2) and testosterone(T) were determined in blood in 150 obese girls, 150 normal girls and 150 malnourished girls, aged from 7 to 17 years old. Their ages of menarche were surveyed. The results showed that serum levels of leptin increased with age, and had double peaks. The first peak of leptin was found during the early phase of puberty in all groups. The value of peak were 14.46 micrograms/ml, 8.85 micrograms/ml, 8.60 micrograms/ml in obese, normal and malnourished groups respectively. The second peak of leptin emerged at the end of puberty in the three groups. The level of E2 increased sharply at the eleven years old in three groups, then increased progressively with age. Serum level of E2 did not correlated with leptin. There was a peak level of T at 10 years old in obese groups, as well as normal and malnourished groups. The level of T emerged rise sharply at 12 years old after a decrease in all groups. Serum level of T did not correlated with leptin. It is suggested that leptin may be a more important decisive factor during pubertal development course in girls. The first peak of leptin may be the signal of onset of puberty. The second peak of leptin may be the signal of the end of puberty.