Compound water-sealing sealant

A compound water-sealing sealant comprising a non-water-swelling thermoplastic resin (A), preferably a vinyl chloride resin, and a water-swelling resin (C) obtained by kneading together 10 to 97% by weight of the non-water-swelling thermoplastic resin (A) and 3 to 90% by weight of a water-swelling material (B). The compound water-sealing sealant is molded by the conjoint extrusion molding of the non-water-swelling thermoplastic resin (A) and the water-swelling resin (C). The water-swelling material (B) is a water-swelling urethane resin which is a prepolymer having isocyanate groups in which the content of terminal NCO groups amounts to 1 to 12%, preferably 2 to 7%, obtained by the reaction of polyisocyanate with at least one polyether polyol of the formula R[(OR1)n OH]p wherein R is a polyhydric alcohol residue; (OR1)n is a polyoxyalkylene chain comprising oxyalkylene groups each having an oxyethylene group and an alkylene group carrying three or four carbon atoms, and wherein the content of the oxyethylene groups is 20 to 100% of the total molecular weight; n is a number corresponding to the degree of polymerization of the oxyalkylene groups and giving a hydroxyl group equivalent of 200 to 2500; and p is 2 to 8, preferably 2 to 4.