A novel redox system, potassium diperiodatonickelate (Ni(IV))-casein is used to initiate graft copolymerization of Styrene onto casein under different conditions in aqueous alkaline solution. Graft copolymers with both high grafting efficiency (> 98%) and percentage of grafting(> 300%) are obtained, which indicated that (Ni(TV))-casein redox pair is an efficient initiator for this grafting. The effects of reaction parameters, such as monomer-to-casein weight ratio, initiator concentration, pH, time, and temperature, are investigated. A tentative initiation mechanism is proposed. The structures and properties of the graft copolymer are characterized by Fourier transform infrared Spectroscopy, X-ray diffraction diagrams, and Scanning Electron Microscope. (c) 2006 Wiley Periodicals, Inc.