Poly(acrylonitrile-methylmethacrylate-sodium vinylsulphonate) membranes were subjected to modification by grafting of 2-dimethylaminoethyl methacrylate (DMAEM) and 2-acrylamido-2-methylpropanesulphonic acid (AMPSA). An Fe2+ H2O2 system was used to initiate the polymerization. Reaction time, temperature, pH, and concentrations of an initiator and modifying agent were the variable parameters. Tertiary amino groups, quaternary ammonium groups, and sulfo groups were determined quantitatively by potentiometric titration. The degree of grafting and hydrophilicity and charge density of the modified membranes were studied. Glucose oxidase was immobilized onto modified acrylonitrile copolymer membranes with DMAEM and AMPSA and showed high relative activity. The amount of bound protein and storage of the activity of the immobilized enzyme were determined.