Abstract: Early sound exposure effects on the characteristics of frequency tuning of inferior collicular (IC) neurons in Myotis chinensis,were examined with electrophysiological technique.The units tuned to exposing frequency in animals exposed at the first and third postnatal week showed stronger clustering compared to the control and those exposed at the fifth postnatal week.The tonotopic organizations and Q10-Db values of the units were also abnormal.This could be interpreted as the result of the over-representation of corresponding region in basilar membrane and then transmitting along the central auditory pathway.It meant the synaptic plasticity during postnatal development.Thus,we believed the critical changes of auditory development appeared to take place within the first 4 weeks after birth.