Polyester resin, and aqueous dispersion prepared using same

The present invention is a polyester resin composed of carboxylic acid components and alcohol components, wherein (A) a dicarboxylic acid component having no sulfonate salt group is contained in an amount of 50 to 100 mol%, (B) a glycol component having no sulfonate salt group is contained in an amount of 50 to 100 mol%, (C) a sulfonate-salt-group-containing monomer component having one ester-reactive functional group is contained in an amount of 3 to 30 mol%, and (D) a compound component having at least three functional groups is contained in an amount of 1 to 20 mol% wherein the total amount of all of the carboxylic acid components is 100 mol% and the total amount of all of the alcohol components is 100 mol%, and wherein the ratio of the amount of the component (C) to the amount of the component (D) falls within a specified range. The polyester resin can exhibit excellent water resistance even when an ionic group is introduced into the polyester resin to such an extent that the resultant polyester resin can be dispersed in water.