Objective:To study the change of the expression of heat shock protein 70 and ultrastructure of brain in sleep deprivation(SD).Methods:44 male Sprague-Dawlay rats were randomly divided into 11 groups.The HSP70 positive cells were detected by using immunohistochemical methods.The ultrastructure of hippocampal neuron was observed through electromicroscope.Results:HSP70 were detected in the cerebral cortex and hippocampus after SD.The HSP70 could be found after 12 h SD,reached to a peak during 2-3 d SD,and declined after 7 d SD.The number of HSP70 positive cells of SDd12h group was markedly more than that of SDn12h group(P