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Background: REM sleep has a role in memory processing. The period of post-learning, that REM sleep is higher than normal level and deprivation of REM sleep impairs memory, is called paradoxical sleep windows (PSW). Methods and Materials: In this experimental study, male N.M.RI rats were trained in a two-way shuttle avoidance task (100 trials/one sessions) then memory retention was tested in next week. In electrophysiology section, different sleep-memory factors were recorded in basal level and 1-4 hours after training. In behavioral section, animals that reached 70% learning criterion (learner group) were deprived of PS in the two periods of 1-4 hours and 5-8 hours after learning by Maze water technique. Results: The amount of REM sleep in group which gained 70% learning after 1-4 hours training, and group without it. In v.s of basic level, significantly increase (p0.01). Other factors were showed no significant difference between two groups before of training. In behavioral section those animals were deprived in 1-4 hr post-learning show significant memory impairment (p0.05). Conclusion: Paradoxical increased REM sleep is effective in memory consolidation after 1-4 hours training. This period can be consider as paradoxical sleep window.