Rapid-eye-movement (REM) sleep behavior disorder (RBD) is a parasomnia characterized by complex motor activity associated with dreaming during REM sleep. RBD may be idiopathic or associated with various neurological diseases involving the brainstem. The association of RBD and limbic system impairment was unclear. We report a 46-year-old man with acute aseptic limbic encephalitis in association with RBD. The patient presented with subacute onset of anterograde/retrograde amnesia and persistent fever. Abnormal nocturnal behavior during sleep consisted of waving hands to fight and kicking legs. Brain magnetic resonance imaging showed damage on the bilateral unci and medial temporal lobes. Cerebrospinal fluid analysis indicated aseptic encephalitis. A polysomnography revealed augmented phasic activity in the submental and bilateral tibialis anterior muscles during REM sleep. Our finding suggests that limbic system impairment may lead to the occurrence of RBD.