Disclosed is an agent for ameliorating or preventing metabolic syndrome which comprises, as the active ingredient, a degradation product of ß-1,3-1,4-glucan that has a weight-average molecular weight of 1000 Da or more and less than 50000 Da. The aforesaid agent for ameliorating or preventing metabolic syndrome, which has a high biological safety and can be continuously taken everyday, is usable as a component of medical drugs, foods, drinks and so on. Also disclosed are a novel composition which is usable in preparing the aforesaid agent for ameliorating or preventing metabolic syndrome, and a method for producing the same.
