The Mn3+ initiation system has been used to prepare starch-g-polyacrylonitrile copolymers. Both granular native starch and water-swollen gelatinized starch have been used as substrate. Conversion of monomer, graiting ratio, and percent add-on tend to increase with increasing amounts of monomer charged. The amount of homopolymer formed is extremely low, a p proximately 1%. The efficiency, measured as conversion, is consistently higher with gelatinized starch as Substrate. The molecular weight of the grafta on gelatinized starch is approximately eight times higher than those on granular starch. Granular starch has a correspondingly higher frequency of grafta. Solubility measurements of starch, polyacrylonitrile, and grafted starch were carried out in dimethylsulfoxide (DMSO) at 348 K. Starch and polyacrylonitrile were totally soluble in DMSO under the chosen conditions. The solubilities of grafted samples were independent of the state of the substrate before grafting and of molecular weights of the grafted chains, but were found to be correlated to percent add-on. Starch-g-polyacrylonitrile samples, with gelatinized starch as substrate, were saponified in aqueous sodium hydroxide eolution. The water retention value increased linearly with increasing add-on. The saponified polyacrylonitrile, branches alone had a water retention value that was three times higher than that of the original copolymer.