Objective To study the effect of chloral hydrate on click sound evoked auditory brainstem re-sponse (ABR) in healthy adult guinea pig .Methods A total of 20 healthy wild type albino male guinea pigs were se-lected for ABR assessment with click sound stimulation conscious and cholral hydrate anesthesia conditions .The ABR threshold was determined according to the wave that presents highest occurrence rate under different stimulus intensity .The latency ,interpeak latency of each wave at 90 dB peSPL stimulation as well as the amplitude of waveⅡ ,Ⅲ ,Ⅳ under different stimulus intensity were recorded .Results The ABR threshold in chloral hydrate anes-thesia was 25 .50 ± 2 .76 dB peSPL and at the waking state was 28 .5 ± 3 .66 dB peSPL from control group (P>0 .05) .The latencies of each wave recorded under chloral hydrate anesthesia state were prolonged compared to those of under waking state ,wave Ⅲ ,Ⅳ and Ⅴ had significance differences (P<0 .05) ,but wave Ⅰ ,Ⅱ had no significant differences (P>0 .05) .The interpeak latency between wave Ⅰ - Ⅴ ,Ⅲ - Ⅳ ,Ⅳ - Ⅴ in chloral hydrate anesthesia were longer compared to those of under waking state with significant differences (P<0 .05) ,while interpeak latency between Ⅰ - Ⅱ ,Ⅱ - Ⅲ had no significant differences (P> 0 .05) .The amplitude and occurrence rate of wave Ⅱwere the highest among all the waves in both experimental group and control group .The amplitude of wave Ⅱ and Ⅲ in chloral hydrate anesthesia was higher than that of the waking state under acoustic stimulation conditions ofhigh intensity(P<0 .05) while the amplitude of wave Ⅳ was lower than the waking state (P<0 .05) .Conclusion The chloral hydrate anesthesia may be able to apparently lengthen the ABR latencies of wave Ⅲ ,Ⅳ ,Ⅴ and affect the amplitude .This effect should be considered during the assessment of ABR under anesthesia state in guinea pig ;The ABR threshold of guinea pig could be determined according to the wave Ⅱ because it 's highest occurrence rate .