The purpose of the present invention is to provide a highly safe composition that improves glucose tolerance and sugar metabolism at skeletal muscles, and a prevention/treatment drug for diabetes/metabolic syndrome containing the composition. Provided is a composition that is for improving sugar metabolism and glucose tolerance and that contains a compound represented by formula (I) derived from a plant selected from the group consisting of Rumex japonicus, R. crispus, and R. obtusifolius as the active ingredient.
