Polymer composites based on biodegradable polymers and natural-organic fillers are becoming more and more important because of their interesting properties in terms of environmental impact, manufacturing cost, and esthetic features. In particular, the use of biodegradable polymer matrices allows obtaining a full biodegradability. One of the most interesting biodegradable polymer families is the Mater-Bi (R) one. In this work, we investigated the processability, the influence of different processing techniques, and the influence of the filler particle size on the properties of Mater-Bi/wood flour composites. Injection molding caused a partial degradation of the macromolecular chains, whereas single-screw extrusion followed by calendering and twin-screw extrusion provoked an increase of the elastic modulus and of the viscosity. The use of wood flour led to a significant increase of the rigidity, whereas a reduction of the ductility was observed. Because of the very similar aspect ratios of the two different filler size classes, no dramatic differences in the properties were found. These results are useful in order predicting and setting up the optimum preparation and processing strategy for the production of fully biodegradable polymer composites. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 114: 2855-2863, 2009