Wood Plastic Composite (WPC) has attracted great interest in outdoor building products for the reduced cost and the possibility of using recycled materials. Nevertheless the material shows two problems: the large viscosity due to the presence of high concentrations of filler and the degradation of cellulose during processing The aim of this work was to investigate the rheological and thermal properties of WPC. The material used for the experiments was a commercial PP-based WPC compound, with different concentrations of natural fibers (30, 50, 70% wt.). The thermal properties were studied to check for degradation of natural fibers during the subsequent rheological tests. Analyzing the storage and loss moduli and the complex viscosity curves obtained using a parallel plate rheometer it was possible to observe some features related to the viscoelastic nature of the composite.