In this article, graft copolymerization of styrene (St) onto cassava starch via potassium diperiodacuprate (III)Âstarch redox system as an initiator was investigated in an alkaline medium. The graft copolymer was characterized with Fourier-transforminfrared spectra analysis (FTIR), thermal gravimetric analysis (TGA),X-ray diffraction (XRD) and scanning electronmicroscopy (SEM). FTIRspectra indicated the presence of PSt-g-starch copolymer. XRD analysis exhibited insignificant changes in crystalline structure and degree of crystallinity. SEMmicrographs also showed PSt adhering on the starch.A mechanismwas proposed to explain the generation of radicals and the initiation. The effects of reaction variables were investigated, and the grafting conditions were optimized. The value of the overall activation energy of styrene-starch polymerization (49.4kJ/mol) and the equation of the polymerization rate were obtained, Rp= k·C1.09 (St)C0.50 (Cu (III)).