Based on the results of graft copolymerization to proteins, an attempt is made to derive the rate equations to explain the mechanism of Ce(IV) ion-initiated graft copolymerizations. In this system the oxidative termination by Ce(IV) $[R{cdot}+ Ce(IV) ${ ightarrow}$ R(inert) + Ce(III) + H^+]$</TEX> is considered characteristic particularly in higher concentration of Ce(IV) ion. The change in the mode of termination reactions with change in Ce(IV) ion concentration makes possible the presence of an optimum Ce(IV) ion concentration for maximum graft copolymerization yield. This effect is reflected in presently derived equations