Graft copolymer(SSPA) with high water absorbency was prepared by saponification of soluble starch-g-polyacrylonitrile (SPA) , having different molecular structure. The water absorbency of the saponiaed derivative was discussed in relation to the structural parameters. SSPA of diversified molecular structure was obtained by controlling the reaction conditions of graft polymerization of acrylonitrile onto soluble. Starch, initiated by Ce(IV) -starch redox system, acid hydroysis and saponification of SPA. It has been revealed that 1) the content of Na carboxylate, 2) graft chain length, and 3) % graft are major factors, increasing the water absorbency of SSPA. In order to elucidate the effect of starch backbone polymer on the water absorbency of SSPA a calibration curve for the determination of starch content in SSPA was developed by means of IR measurement which led to the conclusion that the water absorbency of SSPA is independent on the content and structural characteristics of starch.