The present invention provides a carboxyl group-containing polymer composition that exhibits excellent anti-soil redeposition ability in fabric washing. The carboxyl group-containing polymer composition contains a carboxyl group-containing polymer, which includes specific ratios of a structure unit (a) derived from an acrylic acid-based monomer (A) and a structure unit (b) derived from a sulfonic acid group-containing monomer (B) and has a specific weight average molecular weight, and a specific amount of an adduct of a hydrogen sulfite to the acrylic acid-based monomer (A).