The invention relates to a coating agent composition comprising an isocyanate-group-containing prepolymer obtained by reacting a polyol comprising a polyoxyalkylene polyol having 2-4 hydroxyl groups on average, an oxyethylene group content of 85-100% by mass based on all oxyalkylene groups (100% by mass), and an arithmetic-average molecular weight of 800-2,500 with an alicyclic isocyanate and/or an aliphatic isocyanate in the presence of an organic acid bismuth salt catalyst, the isocyanate(s) being used in such an amount as to result in an isocyanate index of 150-300. The invention can provide a coating agent composition which forms a coating film or film having moisture permeability, excellent in mechanical properties and yellowing resistance, having laundering durability and resistance to sweat deterioration, and containing no organotin compounds.