Graft copolymerization of acrylonitrile (AN) onto defatted pineapple leaf fiber (PALF) was studied using a CuSO4 and KIO4 combination as an initiator in an aqueous medium in the temperature range 30-50 degrees C. The effects of the concentration of potassium periodate, CuSO4, and monomer on the graft yield were investigated. The effects of time, temperature, amount of some inorganic salts, and organic solvents on the graft yield are also reported. A combination of Cu2+-IO4- in an aqueous medium with an IO4- concentration of 0.005 mol L-1 and Cu2+ concentration of 0.002 mol L-1 produced optimum grafting for use of 0.1 g defatted PALF with a fiber-to-liquor ratio of 1:50 at 50 degrees C for 2 h. However, KIO4 and CuSO4 failed to induce polymerization of AN in the presence of PALF when used separately. FTIR and thermogravimetric analysis of the defatted and AN-grafted PALF were carried out. Grafting improved the thermal stability of PALF.