Effects of wood powder (WP) on mechanical properties of PP/WP composites were studied, and interfacial compatibility between polypropylene (PP) and WP was investigated with SEM. All PP/WP composites were compounded in a parallel twin-screw extruder. Mechanical properties of composites were characterized by tensile, hardness, and impact testing. The result showed that interfacial compatibility in PP/WP composite was ameliorated efficiently by PP-g-(MAH-St) compatilizer, mechanical properties of PP/WP composites were improved by pre-treating WP with alkali and coupling agent. They were also influenced by WP size and WP amount, which were the best at the size of 60-mesh and the amount of 40 wt%.