Composites made of polypropylene, a mixture of polypropylene and poly(lactic acid) and spruce wood fibres both non-modified and modified with toluene 2,4-diisocyanate – were prepared by melt blending. The chemical modifications of wood fibres with toluene 2,4-diisocyanate were evidenced by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Wood fibre reinforced polypropylene/poly(lactic acid) composites prepared with addition of maleic anhydride polypropylene as coupling agent were further investigated for structural and morphology properties before and under controlled accelerated weathering conditions by attenuated total reflectance Fourier transform infrared spectroscopy, mechanical testing and scanning electron microscopy analysis. Some specific indexes (carbonyl and vinyl) were also calculated.