kappa-Carrageenan-g-PMMA copolymer has been synthesized by copolymerizing kappa-carrageenan with methyl methacrylate (MMA) in aqueous medium at about PH 7. The copolymerization was carried out under microwave irradiation in the presence of a water-soluble initiator potassium persulphate. Optimum microwave irradiation conditions for obtaining maximum yields are described. The structural characteristics and thermal stability of kappa-carrageenan-g-PMMA was studied by FTIR, NMR, and thermo gravimetric (TGA) measurements. Crystallinity of the copolymer was studied by powder X-ray diffraction. TGA, IR, and XRD data indicated that the K-carrageenan was considerably modified. Optical micrograph of the copolymer was also studied. A probable mechanism of formation of the copolymer is proposed. (c) 2006 Wiley Periodicals, Inc.