The processes of ZnCl2selective sorption by macromolecules of polymethyl methacrylate and polybutyl methacrylate in binary mixtures with ZnCl2have been studied using light scattering and equilibrium dialysis methods. It has been shown that to a certain concentration of ZnCl2, its average concentration in the volume of macro-molecular coils is equal to that of the complexing agent in the solution, i.e., the parameter of the selective sorption β = 0. However, for the system PBMA-BMA-ZnCl2with increasing [ZnCl2], a negative value of β is observed. After the “threshold” concentration of [ZnCl2]: methyl methacrylate = 0.08, butyl methacrylate = 0.15, an increase in the selective sorption of ZnCl2concentrations is found. The interaction of ZnCl2with macromolecules of polymethyl methacrylate and polybutyl methacrylate is accompanied by a change in the steric parameter and in the thermodynamic quality of the solvent. A probable mechanism of ZnCl2interaction with polymer coils is discussed.