To provide a method for manufacturing a carboxyl group-containing polymer with a narrow molecular weight distribution by subjecting a carboxyl group-containing vinyl monomer to living radical polymerization.

A carboxyl group-containing polymer manufacturing method, characterized in that a vinyl monomer having a carboxyl group in its molecules are subjected to a living polymerization reaction by the atom transfer radical polymerization method. The polymerization initiator preferred for this reaction comprises a rhodium complex and an organic halogen compound or a ruthenium complex and an organic halogen compound.