Graft copolymerization of delignified Grewia optiva fiber with methyl methacrylate (MMA) as vinyl monomer was attempted using ascorbic acid/H2O2 as redox initiator. Different reaction conditions affecting the grafting percentage (P-g) were optimized to get the maximum P-g (32.56%) of MMA onto delignified Grewia optiva fibers. Grafted and ungrafted fibers were subsequently subjected to evaluation of physico-chemical properties such as swelling behavior and acid and alkali resistance. The rate expression for the grafting reaction (R-g=k [ASC](0.12) [H2O2](0.53) [MMA](0.05)) was evaluated and a suitable mechanism for grafting was suggested. The overall activation energy of the copolymerization reaction was found as 11.97 kJ mol(-1) at temperature range 25-65 degrees C. Further, morphological and structural analysis of raw, delignified, and grafted Grewia optiva-g-poly(MMA) were studied by using Fourier-transform Infrared spectroscopy, scanning electron microscopy, X-ray diffraction, and thermogravimetric analysis.The tensile properties of grafted and ungrafted fiber samples were also reported. POLYM. ENG. SCI., 55:474-484, 2015. (c) 2014 Society of Plastics Engineers