The present invention relates to an Agathobaculum sp. strain having a preventive or therapeutic effect on autism spectrum disorders and a use thereof. The gut microorganism Agathobaculum sp. strain according to the present invention exhibits the effect of remarkably alleviating autism spectrum disorders including repetitive behavior, hyperactivity, difficulties with social interaction, and cognitive/memory impairment behavior in valproic acid (VPA)-induced autism model mice and BTBR autism model mice to which the strain has been orally administered, compared to a non-treated control, and thus can be effectively used in a food, a medicinal product, or foodstuff for preventing or treating autism spectrum disorders, finding very useful applications in related industries.