Composites containing linear low-density polyethylene/polyvinyl alcohol and various loadings of kenaf fiber were prepared using a Haake internal mixer. The loading of kenaf fiber varied from 10 to 40 parts per hundred resin (phr). The coupling agent 3-(trimethoxysilyl)propyl methacrylate (TMS) was evaluated for its effect on the processing torque, tensile properties, morphology, water resistance, and thermal properties of the composites. Composites without TMS were used as the control. The composites made from TMS-treated kenaf yielded higher stabilization torque, tensile strength, tensile modulus, water resistance, and thermal properties than the control composites. The improvements were attributed to the coupling effect of TMS.