To provide a waterstop sealing material which excels in the interfacial adhesion between the waterstop sealing material constituted of a foam structure having closed cells and a target structural member for the water to be shut off, makes workability easy, and enhances safety, environmental hygiene, and reliability.

The waterstop sealing material is obtained by laminating a hot-melt adhesive sheet (B) having a plurality of irregularities showing a geometric pattern on at least one surface of a foam structure (A) having closed cells which uses a thermoplastic resin as the major raw material, and all projections forming the periphery of each of the above irregularities have the same height and are narrow and have a nearly equal width, and when the above projections come into contact with the interface of a target structural member (C) for water to be shut off, the compressive force caused in the foam structure is exhibited to the full through the projections to seal the interface between the waterstop material and the target structural member for water to be shut off.