The invention provides a drag reducer having an excellent frictional drag-reducing effect on an aqueous medium and the like and also provides a fire-extinguishing agent including this drag reducer. The drag reducer according to the present invention includes a polyalkylene oxide aqueous dispersion that includes a polyalkylene oxide, aluminum oxide, an electrolyte, and water, and that has the polyalkylene oxide dispersed therein. The drag reducer has an excellent frictional drag-reducing effect on an aqueous medium and the like.