The electron-beam preirradiation and reactive extrusion technologies were used to prepare maleic anhydride (MAH)/vinyltrimethoxysilane (VTMS)-co-grafting polypropylene (PP) as a high-performance compatibilizer for wood-flour/PP composites. The grafting content, chemical structure, and crystallization behavior of the compatibilizers were characterized through Fourier transform infrared spectroscopy, differential scanning calorimetry, and an extraction method. The effects of the compatibilizers on the mechanical properties, water absorption, morphological structure, and torque rheological behavior of the composites were investigated comparatively. The experimental results demonstrate that MAH/VTMS-g-PP markedly enhanced the mechanical properties of the composites. Compared with MAH-g-PP and VTMS-g-PP, MAH/VTMS-g-PP clearly showed synergistic effects on the increasing mechanical properties, water absorption, and compatibility of the composites. Scanning electron microscopy further confirmed that the adhesion and dispersion of wood flours in the composites were effectively improved by MAH/VTMS-g-PP. These results were also proven by the best water resistance of the wood-flour/PP composites with MAH/VTMS-g-PP. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 402-409, 2011