This work focuses on the use of peanut shell powder (PSP) as filler in natural rubber (NR). Peanut, one of the food crops in the world, generates large amounts of waste namely peanut shell. Modified and unmodified PSP-NR composites with varying particle size and dosages were prepared by an open mill mixing technique. The processing characteristics and the curing behavior of the composites were determined by Monsanto Rheometer. The technological performance was done by analyzing the tensile strength, tear strength, and hardness of the vulcanizates. The swelling studies were carried out to observe the crosslink density, rubber-filler interaction, and the reinforcing nature of the filler on NR. The observed variation in mechanical properties has been supported by the fractography of the composites obtained by Scanning Electron Microscopy. The result of the study shows that the PSP is most effective filler in NR at 10 parts per hundred (phr) loading. Filler reinforcement ability of modified PSP is more when compared with unmodified PSP; therefore, modified PSP-NR composites shows better physicomechanical properties. (c) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012