Sleep disorders are commonly observed in multiple systemic atrophy (MSA). The rapid eye movement (REM) sleep behavior disorder (RBD) is characterized by loss of normal voluntary muscle atonia during REM sleep. It usually presents during early course, and disappears over the course of disease progression. Sleep-disordered breathing (SDB) is also common sleep disorder in MSA which can be life-threatening, and continuous positive airway pressure (CPAP) treatment is useful in these patients. A 74-year-old woman with MSA presented for nocturnal respiratory disturbance. She had a five-year history of dream enacting behaviors, which had disappeared four months prior. Polysomnography revealed frequent stridor and sleep hypopnea. During the following full nigh CPAP titration for SDB, dream enacting behavior was observed during REM sleep stage. In MSA patients with SDB, CPAP administration may lead to increase REM sleep stage. An increase in REM sleep stage, which previously had been deprived, may have trigger RBD symptoms to reappear. The CPAP treatment should be considered with great caution in these patients.