The graft copolymerization of acrylonitrile onto cotton yarn and viscose rayon with ceric。ammonium nitrate as initiator has been studied． It was shown that the grafting occured readily．and the homopolymerization could be inhibited under proper experimental conditions．The grafting is believed to take place principally through the active centers which are formed on the cellulose substract by the action of ceric ion．It was also shown that the grafting was controlled by the diffusion of the solution tO cellulose．The graf-ting proceeded very rapidly at the begining and then leveled off tO a limiting value，depending on the fine structure of the cellulosic material，as a result of the retar- dation of diffusion by the formation of polyacrylonitrile on the surface of the cellulose．A preliminary estimation was made on the properties of the grafted products．