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Objective Chronic unpredictable stress was commonly used to evoke depression-like behavior in rat.The present study was undertaken to investigate the effect of chronic unpredictable stress on conditioning fear behavior and somatosensory evoked potential (SEP) of rats.The correlation of the conditioning fear behavior and SEP was also evaluated.Methods Twenty-seven male SD rats (weight 190-200 g) were random divided into control group and model group.Rats in model group were subjected to chronic unpredictable stress.Conditioning fear behavior of rats was observed with Freeze monitor system and the latency of somatosensory evoked potential was evaluated with Powerlab system.Results Compared with control group, rats in model group had decreased freezing behavior responded to the sound stimulation during fear memory stage (56.64% ± 13.78%, n =13, vs 69.72% ± 18.10%, n =14, P < 0.05, mean±SD).The latency of SEP decreased in the rats treated with chronic unpredictable stress (70.54 ± 10.13 ms, n =14 vs 78.46 ± 7.80 ms, n =14, P < 0.05), which had the significant difference between the two group rats.The correlation coefficient of the conditioning fear behavior and SEP was positive (r =0.507, P < 0.05).Conclusion Chronic unpredictable stress inhibited conditioning fear behavior of rats, decreased latency of SEP, which suggests chronic unpredictable stress stimulations active the neurotransmitter network system involved with both conditioning fear behavior and SEP.