Provided is an agent for amelioration or prevention of metabolic syndrome, said agent containing, as an active ingredient, ß-1,3-1,4-glucan having a weight-average molecular weight from 50,000 to 500,000 Da. Said agent has a high level of safety with respect to living organisms, can be taken daily and continually, and can be used as an ingredient in pharmaceuticals, foods, drinks, and the like.