The object is to produce a polysaccharide and/or a monosaccharide
efficiently by hydrolyzing a different polysaccharide efficiently. The
hydrolysis of a polysaccharide is an important means for producing a
monosaccharide that can be used as a starting material for the production
of ethanol, the solubilization of a water-insoluble polysaccharide, and
the production of a useful water-soluble low-polymeric saccharide or the
like. For achieving the object, a polysaccharide to be hydrolyzed is
reacted with water in the presence of a carbonaceous material having
sulfonic acid group therein to cause the hydrolysis of the polysaccharide
to be hydrolyzed, thereby producing a other polysaccharide and/or a
monosaccharide.