PURPOSE: To obtain a molded product with a high quality which has a uniform density, no surface defect and little shrinkage through reaction injection molding using an NCO reactive component having specific expanded microspheres.

CONSTITUTION: First, an NCO reactive component containing expanded microspheres, prepared by encapsulating (A) a compound having at least two NCO reactive groups, (B) air and/or nitrogen dissolved in component A at an amount which provides a molded product having a density of at least 0.75 g/cm3 and at least 5% smaller than the density of a molded product prepared by injection molding without using any air and/or nitrogen, (C) up to 4 wt.%, based on the component A, of a polyether siloxane surfactant, (D) up to 45 wt.%, based on the weight of the molded product, of an inorganic filler for reinforcement and (E) a volatile blowing agent in a synthetic thermoplastic resin shell, is mixed with an organic polyisocyanate. Subsequently, this mixture is introduced into a closed mold and allowed to react, and then the product is removed from the mold.