Polymer composite materials based on the Moplen HP400R polypropylene matrix with a filler from walnut shell flour with 30, 40 and 50% content and 200-315 µm and 315-443 µm fraction were produced by the injection method. The effect of filler content was analysed on the processing properties of the composites such as: MFR Melt Flow Rate and the MVR Melt Volume-flow Rate, as well as the temperature of the filler flour decomposition using the TGA thermogravimetric analysis method. The following was also determined: density, hardness, tensile strength and stiffness modulus of elasticity of the materials in question. The obtained composite material was characterised by low density, which increased with the rising filler content. It was found that the applied natural filler has increased the hardness and stiffness modulus of the composite and decreased the tensile strength.