Styrene-butadiene rubber (SBR) composites filled with hemp hurd powder (HP) were prepared with bis(3-triethoxysilylpropyl) tetrasulfide (Si69) as a coupling agent. The effects of the filler content and coupling agent on the curing characteristics and dynamic mechanical properties of the composites were studied. The results indicate that with increasing filler loading, the torque values increased and the curing time decreased. The mechanical properties improved with increasing filled HP content up to 60 phr. Usually, long fibers led to a sharp decrease in the toughness of the composites, whereas short fibers, such as HP, had a positive effect on the elongation at break within the loading range studied. The extent of the filler-matrix interaction and the scanning electron micrographs of the fractured surfaces confirmed that the addition of Si69 improved the interfacial interaction between HP and the SBR matrix, which led to an increase in the maximum torque and the mechanical properties. Moreover, the coupling agent was helpful in dispersing the filler in the rubber matrix. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 681-689, 2011