[Problems] To provide a carboxyl group-containing polymer composition having excellent dispersibility in water or the like, and a neutralized viscous liquid of which has a low viscosity and high transparency. [Solving Means] A carboxyl group-containing polymer composition containing at least one compound selected from the group consisting of (1) a fatty acid A and (2) a fatty acid ester formed between a fatty acid B and a monohydric alcohol having 1 to 22 carbon atoms, in an amount of from 0.05 to 5 parts by mass, based on 100 parts by mass of a carboxyl group-containing polymer, wherein the carboxyl group-containing polymer is obtainable by copolymerizing an α,β-unsaturated carboxylic acid and a compound having two or more ethylenically unsaturated groups.