Abstract: Provided is a polymer capable of more sufficiently achieving the miscibility with surfactants and the effects of enhancing the surface tension-reducing ability of surfactants than conventional polymers used in detergent applications. The present invention relates to a polycarboxylic acid copolymer used in liquid detergent applications, the polycarboxylic acid copolymer containing: a structural unit (a) derived from a polyalkylene glycol monomer (A) represented by the following formula (1), a structural unit (b) derived from a polyalkylene glycol monomer (B) represented by the following formula (2), a structural unit (c) derived from an unsaturated carboxylic acid monomer (C).