PURPOSE: To provide a simple and easy method for producing a water-sol. copolymer wherein a mixture contg. a carboxylated monomer and a monomer having a polyethylene glycol chain is polymerized in emulsion or suspension in water under the control of mol.wt.

CONSTITUTION: A monomer mixture comprising 0.05-30 pts.wt. carboxylated monomer, 1-60 pts.wt. monomer of the formula (wherein R1 is H or methyl; R2 is 1-4C alkyl or phenyl; and (n) is an integer of 2 or higher), and 20-99 pts.wt. monomer copolymerizable with the foregoing monomers is polymerized in emulsion or suspension in water in the presence of a chain transfer agent and by using an azoic polymn. initiator.