This article discusses the methods of interface modification of Composites based on raw wood flakes and high-density polyethylene (HDPE) and the effects of these modifications on composite properties. An HDPE matrix was modified by a reaction with maleic anhydride (MA) in a twin-screw extruder and then compounded with wood flakes to produce wood-polyethylene composites. Wood flakes were modified by a reaction with a silane coupling agent in an aqueous medium before being compounded with HDPE to produce silane-modified WPCs. Differential scanning calorimetry and Fourier transform infrared spectroscopy data provide evidence for the existence of a polyethylene (PE)-silane-grafted wood structure, which acts as a compatibilizer for wood flakes and PE. The results of MA-modified composites indicate that some maleated HDPE is reacting with wood through esterification to form a compatibilizer for wood flakes and HDPE. Significant improvements in tensile strength, ductility, and Izod impact strength were obtained. Scanning electron micrographs provide evidence for strong interactions between the wood flakes and the matrix agent. The results indicate that 1-2 wt % MA modification on HDPE and 1-3 wt % silane treatment on wood flakes provide WPCs with the optimum properties.