an uncured polyurethane coating formed by applying polyurethane paint containing isocyanate prepolymer on a substrate is cured by a method which comprises applying a catalyst on the uncured polyurethane coating and subsequently exposing the polyurethane coating to a heating atmosphere of 60 ° to 100 ° c . by this method , the reaction of urethanation explosively proceeds and the time for curing the coating can be notably cut because the optimum catalyst for the polyurethane coating can be selected without restriction and the catalyst in a highly concentrated state can be brought into contact with the polyurethane coating .