Abstract: A process for preparing polyurethane foams excellent in durability, elasticity and dimensional stability is disclosed. An unsaturated polyester is prepared through the reaction of an unsaturated dicarboxylic acid with a polyhydroxy compound having at least three reactive hydrogen atoms. The polyester is homopolymerized or copolymerized with other vinyl monomers to produce a homopolymer or a homocopolymer. The polymer or the copolymer is used either alone or together with the polyol as a polymer-polyol for the preparation of polyurethane foams.