Fibre length and width development were monitored for a novel procedure of combined wood chip defibration and wood-polymer compounding as well as further process steps for the production of wood fibre-based composites by applying an image analysis-based particle size measuring technique. While fibre dimension was maintained at a common level after refiner compounding, pelletizing was found to reduce both fibre length and width to about 50% of its initial dimension after refiner compounding. Subsequent injection moulding led to an additional fibre length reduction.