This article discusses the mechanical properties of different composites based on pine, oak wood, rapeseed straw and isotactic polypropylene. The surface of the filler was modified with acetic anhydride to enhance the compatibility between hydrophilic lignocellulosic components and hydrophobic polypropylene matrice. After treatment, mixtures of PP with 30% of the natural components were extruded and injection molded. Tensile strength of composites was not improved by the rapeseed straw chemical modification. However, chemical treatment was successful in improving the strength of the wood in the PP matrice. The results concerning mechanical properties of composites, their aesthetic quality and possibility of their application in various fields indicate an opportunity of production of polypropylene/lignocellulosic composites. Moreover, rapeseed straw so far have been considered as waste materials in plastics industry.