To prepare a polyester polyol in which a lactone is ring-opening addition polymerized with the compound represented by formula (I). (wherein each of A1 and A2 represents an alkylene group having not less than 2 carbon atoms, A3 represents an alkylene group, X represents a cationic component, and each of n and m represents an integer of not less than 1.)The polyester polyol has a high hydrophilic group and high solubility in a solvent (particularly, a low-boiling organic solvent used in the production of a polyurethane) and can design an aqueous polyurethane desirably and produce the aqueous polyurethane.