Biocomposites of styrene butadiene rubber (SBR) reinforced with silane-treated peanut shell powder (SPSP) of different filler loadings and particle sizes were prepared by two roll mixing mills with sulfur as a vulcanizing agent. The cure characteristics of composites were studied, and they vulcanized at 160 A degrees C. Test samples were prepared by compression moulding, and their physicomechanical properties, such as tensile strength tear strength, modulus, hardness, and abrasion resistance of SBR vulcanizates, were studied with filler loading 0, 5, 10, 15, and 20 parts per hundred rubber (phr). Composites with 10 phr filler having small particle size exhibited better properties. The interfacial adhesion between filler and matrix has a major role in the properties of composites. Surface modification of PSP was done by silane coupling agent to improve the interfacial adhesion and it characterised by FTIR, XRD, TGA, UV, and SEM. Better properties are shown by the composites with SPSP. Thermal stability of the composites was also determined using thermogravimetric analysis.