Glycidyl methacrylate (GMA) has been grafted onto Kapok fiber (plant fiber) under irradiation with 60Co gamma rays. Graft polymerization of GMA onto polymer substrates is advantageous because the epoxy group of GMA is modified easily, provide functions such as ion exchange and adsorption of toxic gas, with the original properties remaining intact. The Kapok fiber used in this study was treated with NaClO2 to remove phenolic compounds (especially, lignin). This treatment was verified by observation of both the lignin content and the total alkaline nitrobenzene oxidation yield. The absorbed dose ranged from 40 to 100 kGy and the dose rate was 10 kGy/h. The grafting experiments were performed in a glass ampoule having a cock, with the methanol, followed by the GMA. The irradiated Kapok fiber was immersed in the monomer solution and purged with bubbling nitrogen. Grafting copolymerization was conducted at temperatures of 30 and 60℃. The effects of the absorbed dose, monomer concentration, temperature, and reaction time on the degree of grafting were investigated. The grafting yield increased with increasing temperature, reaction time, and irradiation dose. A relatively higher temperature was required to obtain a high grafting yield. The physical and chemical properties of the GMAgrafted Kapok fiber were investigated using IR spectroscopy, SEM, and TGA. The characteristic vibrations of the carbonyl group increased upon increasing the grafting yield. These results clearly indicate that GMA had been grafted onto Kapok fiber.