The covalent immobilization of bovin serum albumin (BSA) onto maleic anhydride-alt-methyl vinyl ether copolymers (MAMVE) was successfully achieved under aqueous conditions. The grafting reaction was shown to be controlled by attractive electrostatic interactions and so took place at a low salt concentration. Under these conditions, the covalent binding reaction was quite efficient, reproducible, and complete within 20 min. The maximum loading capacity of the polymer was of 20 BSA molecules per polymer chain. This preliminary study demonstrated that the immobilization of proteins in an aqueous medium could be an efficient process, despite the existing hydrolysis of the functional polymer by water molecules.