Increasing environmental concern in developed countries has supported the search for greener building materials. In this regard, using materials from renewable resources is of great interest, including the case of wood-plastic composites in replacement of fiberglass-reinforced composites. Since in the Mediterranean regions annual plants are more abundant than wood forests, in the present work, agroforestry wastes were used as reinforcing elements in composites. Specifically, rapeseed wastes were used to produce polypropylene copolymer based composites. The mechanical behavior of the resulting composites was studied, as well as the influence of a coupling agent in the formulation. From the results, rapeseed sawdust exhibited reinforcing capacity and was considered a plausible substitute for wood-plastic composites in certain uses. The stiffness of the composites was affected by the coupling agent, as the Young’s Moduli progressed from 3.2 to 4 GPa for the formulation containing 50wt% of rapeseed sawdust. Micromechanical analysis was used to identify the contribution of each phase by means of a modified rule of mixtures and Halpin-Tsai equations. The micromechanical study confirmed the competitive stiffening capability of rapeseed sawdust in composite materials.