PURPOSE: To obtain a waterproof sheet which is harmless for the human body, by a method wherein a raising fiber layer is provided on a sheet of synthetic resin with an acetalized polyvinyl alcohol single fiber whose degree of the acetalization is specific.

CONSTITUTION: A waterproof sheet is constituted by providing a raising fiber layer comprised of an acetalized polyvinyl alcohol single fiber whose degree of acetalization is 20-50% on one side or both sides of a synthetic resin or synthetic rubber sheet. For example, polyethylene, ethylene-vinyl acetate copolymer and polyvinyl chloride and styrene-butadiene rubber and ethylene-propylene rubber can be mentioned respectively as synthetic resin and synthetic rubber. Since an acetalized polyvinyl alcohol single fiber whose degree of acetalization is 20-50% constituting a raising fiber layer is superior in affinity for concrete or mortar, the same has strong adhesion to the concrete or the mortar and is superior in water resistance, alkali resistance and weather resistance and harmless for the human body by differing from asbestos.