Abstract: Newborn SD rats were divided into three groups：one group for control and two for experiments. Young rats were exposed to high-intensive pure-tone （4kHz,80db spl）for 12 h daily from postnatal days 1 and 9. The changes of succinic dehydrogenase activity of the hair cells of basilar membrane were studied at about 90 days after birth.We found that two experimental groups succinic dehydrogenase activity of the hair cells of middle turn basilar membrane decreased when compared with that of control group, especially the outer hair cells.The histochemical changes of the succinic dehydrogenase activity suggest that the disturbance in energy metabolism is closely associated with postnatal exposure of high-intensive pure-tone.While the single unit responses to pure tone stimuli at dorsal cochlear nucleus （DCN） neurons were studied electrophysi-ologically,the distribution of best frequency （BF）of units from postnatal days 1 and 9, when compared with the control group,showed an abnormal lossing centered around the region of the audiogrom occupied by the tones to which the annimals had been exposed. The results suggested that postnatal exposure of high-intensive pure-tone directly damaged the corresponding region of the basilar membrane of the cochlear，and dereased pro-jection to the higher central auditory nucleus.As a result,units of the corresponding re-gion of the dorsal cochlear nucleus were missing. The result of this experiment indicates that the damage of the auditory system is getting more serious with earlier exposure.

Key words: Sound exposure, Succinic dehydrogenase, Dorsal cochlear nucleus, Best frequency, Rat