As a new strategy to effectively use wood and plastic wastes, composites of high content wood flour (WF) and recycled high density polyethylene (RHDPE), with and without maleic anhydride polyethylene (MAPE) as compatibilizer, were prepared by direct extrusion using a twin-screw/single- screw extruder system. The effects of MAPE on the properties of composite were investigated by mechanical tests, torque rheological analysis, scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). The results demonstrated that MAPE greatly improved the mechanical properties of the prepared WF/RHDPE composites. This was attributed to the strong improvement effects of MAPE on the interfacial interaction of the composites, as was confirmed by the torque rheological and SEM analysis. According to the DSC results, composites with 60% WF content show lower crystallinity degree (Xc) and melting temperature (Tm) than RHDPE, but the values for Tm and Xc did not have noticeable changes with the addition of MAPE.