Abstract: A process for producing a urethane foam having a high density outer surface layer, of the type wherein a plastic liquid containing aromatic isocyanates, polyols, a catalyst, low-molecular polyols used as a crosslinker or a chain extender, a blowing agent consisting of water, and an assistant is poured into a closed mold through a one-shot molding process, a certain type of catalyst is added to create a difference in gas evolving reaction between an inner part and an outer part of the plastic liquid within the mold so as to form a high density layer on the outer surface of a urethane form. The catalyst includes a piperazine compound, a morpholine compound, or a mixture thereof. An imidazole compound, a triazine compound, an amidine compound or an organic acid salt of the amidine compound, or a mixture resulting from any combination thereof may be used in combination with the piperazine compound or a morpholine compound.