Polyester polyols each having structural units of both general formulae (I) and (II) in the molecule; and polyurethanes produced from the polyester polyols. The polyurethanes are excellent in hydrolysis resistance, alkali resistance, mechanical strength, etc. In said formula (I) R<1> and R<2> are the same or different and each represents lower alkyl of 1 to 8 carbon atoms. In said formula (II) R3 and R4 are the same or different and each represents lower alkyl of 1 to 8 carbon atoms.
