The agrowaste of sugarcane bagasse was used as a filler to improve the properties of rubber. Sugarcane bagasse waste was ground and sieved to a particle size less than 75 nm and then purified and chemically modified by an acetylation method and stearic acid adsorption. The modified bagasse was incorporated into styrene-butadiene rubber formulations with different concentrations (20, 30, 50, and 70 phr) in comparison with carbon black and hisil, commercial fillers used in industry. The physicomechanical properties of the rubber vulcanizates were determined before and after thermal aging at 90 degrees C. The retained values of the tensile strength, elongation at break, and equilibrium swelling increased as the concentration of the modified bagasse increased in styrene-butadiene rubber vulcanizates until 50 phr; after this concentration, the retained values of each property decreased. Rubber vulcanizates containing modified bagasse with a concentration of 50 phr may be better for retained values of the physicomechanical properties and equilibrium swelling in comparison with those containing carbon black, hisil, and untreated bagasse. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3470-3476, 2009