Social defeat stress (SDS) plays a major role in the pathogenesis of psychiatric disorders like anxiety and depression.Sleep is generally considered to involve recovery of the brain from prior experience during wakefulness and is altered after acute SDS.However,the effect of acute SDS on sleep/wake behavior in mice varies between studies.In addition,whether sleep changes in response to stress contribute to anxiety is not well established.Here,we first investigated the effects of acute SDS on sleep/wake states in the active period in mice.Our results showed that total sleep time (time in rapid eyemovement[REM]and non-REM[NREM]sleep) increased in the active period after acute SDS.NREM sleep increased mainly during the first 3 h after SDS,while REM sleep increased at a later time.Then,we demonstrated that the increased NREM sleep had an anxiolytic benefit in acute SDS.Mice deprived of sleep for 1 h or 3 h after acute SDS remained in a highly anxious state,while in mice with ad libitum sleep the anxiety rapidly faded away.Altogether,our findings suggest an anxiolytic effect of NREM sleep,and indicate a potential therapeutic strategy for anxiety.