Abstract: To further understand the mechanism of sexual difference of vocalization and the relation among the vocal behavior,vocal control nuclei and testosterone level in the serum,sound spectrogram,volume of three vocal control nuclei (HVC high vocal-control center,RA robutus archistriatalis nucleus and Area X),weight of testis and testosterone levels in the serum were investigated in the songbird (Lonchura striata swinhoei) from post-hatching 5 days to 120 days.The results were as follows:1) Both the male and female produced several kinds of calls before post-hatch 45 days and there was no sexual difference among these calls between the male and female.Male birds began to sing only after post-hatching 45 days.However,they could not sing the same complex and stable songs as the adult males until post-hatch 120 days.Female birds could not produce any song as the male.2) HVC,RA and Area X in the female were 6,4,and 2 times less than the volumes of the corresponding nuclei in the male,respectively.HVC,RA and Area X developed in different ways.Their rapid increasing period was not parallel to the time when the male birds learned singing,indicating that the development of the vocal control nuclei was not completely subjected to the vocal behavior.3) Only the testis developed very well or the testosterone in the serum reached adequately high level,male birds could produce quite complex and stable songs,suggesting that testosterone level in the serum could be one of the important factors in the mature song production.