A biodegradable copolymer was synthesized by grafting copolymerization of acrylamide, -hydroxyethyl methacrylate, and n-butyl acrylate onto corn cationic starch (CS) by microwave irradiation. The grafted cationic starch (GCS) was characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction. The optimum conditions on graft copolymerization with respect to reaction temperature, exposure time, and initiator concentration were investigated. Physicochemical properties of GCS, such as swelling power, solubility, intrinsic viscosity, and apparent viscosity, were studied, and its application performances as textile sizing agent were tested. Results showed that compared with CS, physicochemical properties of GCS were significantly improved, including decreased crystallinity, weakened granular, increased hydration capacity, and rheological property. Polyester/cotton blended yarns sized with GCS obtained more reinforced mechanical properties than samples sized with CS and exhibited higher tensile strength and abrasion resistance than polyvinyl alcohol (PVA) sized yarns. The mechanisms that the starch physicochemical properties affected on the sizing performances were discussed as well. Biodegradation analysis on these sizing agents showed that BOD5/CODcr of GCS was 0.263, which outclasses that of PVA (BOD5/CODcr=0.009). This novel biomaterial could be expected to have promising applications especially in textile industry and be an ideal substitute for PVA. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1645-1652, 2013