PURPOSE: To obtain the titled resin mold excellent in dimensional accuracy, heat resistance, strength, surface smoothness and durability by reacting unsaturated polyester resin on multifunctional isocyanate compound and forming a gel coat and an FRP reinforced layer.

CONSTITUTION: Mixsture of 100pts.wt. of unsaturated polyester resin and preferably 3W50pts.wt. of multifunctional isocyanate compound (such as hexamethylene diisocyanate prepolymer etc.) is applied to a matrix and hardened to form a gel coat. Then, glass fiber is impregnated with the mixture of unsaturated polyester resin and multifunction isocyanate compound. The impregnated glass fiber is laminated on said gel coat, hardened and then removed from the mold to obtain the desired resin mold.