The present invention herein provides a chitosan-containing polysaccharide and a method for the preparation thereof as well as a medicine and a food containing the polysaccharide.The chitosan-containing polysaccharide is prepared by a method comprising the steps of heat-treating a fungus in a concentrated aqueous caustic alkali solution; subjecting the resulting solution to a solid-liquid separation treatment; dissolving the resulting solid contents in an aqueous organic acid solution; adding, to the resulting solution, an alcohol or a caustic alkali to thus form precipitates; washing the resulting precipitates; and then drying them. This chitosan-containing polysaccharide is a compound in which homopolymers of glucosamine are linked with glucan through covalent bonds; it has a molar ratio of glucosamine and glucose constituting the polysaccharide ranging from 1:5 to 5:1; it has a molecular weight of about 150,000; and it does not contain any .beta.(1.fwdarw.3) bonds, but comprises .beta.(1.fwdarw.4) bonds and .beta.(1.fwdarw.6) bonds. The polysaccharide is free of any protein and reducing polysaccharide. The chitosan-containing polysaccharide is effective for the treatment or prevention of any diseases originated from living habits or customs such as hypertension and diabetes.