A starch-based superabsorbent hydrogel with quaternary ammonium and carboxyl groups is synthesized in aqueous solution. Various factors, including the initiator dose, the crosslinker dose, and the dose and the concentration of the acrylate monomer, as well as the polymerization temperature, are investigated in terms of the swelling in distilled water and in a 0.9% NaCl solution. Furthermore, the thermal degradation of the modified starch graft copolymer is studied under an air atmosphere. (c) 2005 Wiley Periodicals, Inc.