Development of polymeric materials with desired properties can ensure effective solution of many technological problems. Preparative procedure of isolation, separation and purification of proteins usually is multistage process. Usage of sorption processes allows diminishing essentially the number of stages and enhancing the quality of the recovered product. Sorbents for protein sorption can be synthetic or based upon polysaccharide matrix. Synthetic sorbents have larger total sorption capacity and osmotic stability, but not always good permeability for large molecules. Carboxylic cation-exchanger K-120 has been developed for sorption of proteins. It has aliphatic matrix containing methacrylic and acrylic acid units and thermodynamically flexible crosslinking agent. The introduction of both acrylic and methacrylic acid units changes the ionization parameters of the cation-exchanger and enhances essentially sorption ability towards proteins.