Abstract: The present disclosure relates to a composition for preventing, alleviating or treating sleep disorder, containing, as an active ingredient, Prevotella histicola, a culture product thereof, a crushed product thereof, an extract thereof or a fermented product thereof; or extracellular vesicles derived from Prevotella histicola. The Prevotella histicola or extracellular vesicles contained in the composition of the present disclosure can be used as a safe drug for preventing and treating sleep disorder by increasing total sleep time, non-REM (NREM) sleep time and REM sleep time and decreasing sleep latency and waking time.