Resin composition and an aqueous resin composition

PROBLEM TO BE SOLVED: To provide an aqueous resin composition capable of being utilized for wide uses including various kinds of aqueous coatings, aqueous inks, adhesives and sealants. SOLUTION: This resin composition comprises (A) a polymer obtained by copolymerizing an ethylenically unsaturated monomer composition containing (a) an ethylenically unsaturated monomer having at least one carboxy group in the molecule and (b) an ethylenically unsaturated monomer having at least one carboxylic acid ester group in the molecule, (B) a compound having two or more hydroxy groups in the molecule, and (C) an onium salt selected from quaternary ammonium salts and quaternary phosphonium salts. The aqueous resin composition uses the resin composition.