In this study the influence of filler particle size (40, 50, and 60 meshes) and coupling agent concentration (0 and 2 wt%) on the composite mechanical properties were studied. Specimens having 30wt% wood flour of poplar were mixed with polypropylene and polypropylene grafted maleic anhydride (PP-g-MA) as coupling agent. It was found that strength properties of the composites can be improved moderately by adding 2wt% PP-g-MA. It was also observed that smaller filler particles provide higher tensile modulus than the larger sized filler. Moreover, increase in aspect ratio of the wood particles contributed to the enhancement in the mechanical properties of the composites. The elongation value was not found to have any considerable variation with particle size. The PP-wood flour composites exhibited low impact strength compared to pure PP. In general, Wood flour could be considered as a potential source of low cost, natural fibers for composites.