To provide a polyisocyanate-curable water-based dispersion coating material (such as water-based polyurethane resin composition) which is improved in the dispersibility of the chief material resin in an aqueous medium and prolonged in the pot life by depressing the reaction of water with isocyanate group (which is highly reactive with water) and which can form a coating film exhibiting excellent surface appearance and water resistance equivalent to those of films of conventional solvent-type polyurethane resin coating materials in spite of its being a water-based coating film. A water-based resin composition comprising (A) a water-based acrylic resin or a water-based polyurethane resin obtained by reacting a diisocyanate with a polyol and (B) a polyisocyanate dispersible in the component(A), characterized by containing (C) a low-molecular-weight compound having a carbon-carbon unsaturated bond and a carbonyl group adjacent thereto.