The medial geniculate body (MGB, the auditory thalamus) receives strong corticofugal modulation that includes facilitation and inhibition. Auditory stimuli evoke an onset response that in many neurons followed by a lasting post response inhibition in MGB neurons. In the present study, we investigated the post response inhibition of MGB neurons in sleeping rats. Chronically implanted electrodes were used to record the neuronal activities of the MGB, as well as, the electroencephalogram (EEG) and the electromyography (EMG) from the rats in different stages of sleep. Both ON and ON-OFF neurons in the MGB showed prolonged post-response inhibition of over 50 ms. The post-response inhibition showed a shorter duration in rapid eye movement (REM) sleep than that in non-rapid eye movement (NREM) sleep. After the auditory sector of the thalamic reticular nucleus (TRN) was reversibly inactivated by local application of lidocaine, the post-response inhibition of MGB neurons disappeared or decreased. Based on these results, we concluded that the TRN was involved in the post response inhibition of the MGB in sleep. The TRN applied stronger inhibition to the MGB neurons during non-REM sleep than during REM sleep.