This study deals with the effect of chemical modification of wood flour by components including alkaline, silane, acrylic acid and benzoyl chloride, and PP-g-MA coupling agent concentration (0 and 3 wt%) on the mechanical performance of WPCs. The samples were fabricated by melt compounding in an internal mixer and then injection molding. Tensile, flexural, and Izod impact test of modified composites were performed and compared by net polypropylene and unmodified samples. The results showed that the highest tensile and flexural resistance was observed in composites modified with alkaline and including coupling agent. Modified composites had lower impact strength than unmodified ones. Simultaneous use of chemical modification and coupling agent on mechanical properties had synergic effect. Therefore, chemical modification of wood flour improved interfacial adhesion and so increased the mechanical performance of these composites.