Graft copolymerization of nitrile monomers, such as acrylonitrile and methacrylonitrile, onto bleached jute fiber was carried out by using K2S2O8/FeSO4 redox system in nitrogen atmosphere and their effect on the textile characteristics was also investigated. Percent graft yield increased with the increase of concentrations of monomer, initiator, and catalyst, reaction time, and reaction temperature up to a certain value, and, thereafter, it decreased. The effect of percent grafting efficiency was similar to that of percent graft yield, except for the monomer concentration. The increase of percent graft yield was dependent on the availability of jute-macroradicals as well as monomer radicals. Sometimes the predominancy of homopolymerization over grafting and the premature termination of growing grafted chains occurred because of the higher monomer radicals and excess primary radicals, SO4-. and (OH)-O-., from K2S2O8 initiator. The percent graft yield of acrylonitrile and methacrylonitrile was 20.5 and 29.1%, respectively. Higher graft yield for methacrylonitrile might be due to the methyl group present in it. Infrared spectra at 2229-2235 cm(-1) of acrylonitrile- and methacrylonitrile-grafted jute strongly supported the graft formation. Grafting of jute fiber improved the thermal stability, protected from photooxidative degradation, and decreased swellability as well as dyeability, etc. (C) 2004 Wiley Periodicals, Inc.