A process is provided for producing a polyurethane foam having a high-density skin layer by reacting a polyol with a polyisocyanate in a short time. The reaction is allowed to proceed in the presence of a blowing agent, a catalyst, and optionally an additive, the blowing agent being composed only of water, and the catalyst being an amine represented by formula (I) below and/or an organic acid salt thereof: ##STR1## where R.sub.1, R.sub.2, R.sub.3, and R.sub.4 are, independently, an alkyl group of 1 to 12 carbons, or R.sub.1 and R.sub.2, and/or R.sub.3 and R.sub.4 may be linked to form a cycloalkyl or heterocyclic ring together with the adjacent nitrogen atom; and R.sub.5 is hydrogen, an alkyl group of 1 to 12 carbons, a phenyl group, or a cycloalkyl group. This process does not use halogenated hydrocarbons which cause ozone layer destruction.