To provide a water-swelling adhesive capable of being furnished with stable adhesive strength by moisture in the atmosphere, and further capable of being swollen by alkaline water after adhesion so as to be decreased in the adhesive strength.

This water-swelling adhesive comprises a moisture-curing prepolymer made from polyethylene glycol, polypropylene glycol and tolylene diisocyanate, and having isocyanate groups at its terminals, wherein the prepolymer contains the isocyanate group in an amount of 2.5-4.0%, has a continuous structure formed by addition polymerization of the polyethylene glycol, the polypropylene glycol and the tolylene diisocyanate, and preferably has no tolylene diisocyanate which exists freely. The composition can be cured to be adhesive at room temperature by the moisture in the atmosphere, and further swollen by the free alkaline water in concrete after adhesion so as to be furnished with releasability, because the prepolymer is made to contain the isocyanate in the amount of 2.5-4.0%. Thus the composition can be easily released while keeping the adhesive strength, when the composition is used for adhering natural stones or the like to a frame for decorative panel.