We have characterized the melt rheological behavior and the solid tensile properties of sawdust/polyethylene composites prepared in an internal mixer. Various concentrations (from 0 to 60 wt %) and three particle sizes have been tested, in presence of a coupling agent (maleic anhydride grafted polyethylene). In the molten state, for each particle size, a mastercurve of the complex viscosity as function of frequency can be plotted, using a shift factor depending oil weight fraction. We show that the shift factors can be described by a Krieger-Dougherty law, leading to a "universal" viscosity law of the Carreau-Yasuda type. In the solid state, the presence of sawdust increases Young modulus in uniaxial elongation, mainly for small size particles, but reduces dramatically deformation at break and tensile strength. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2559-2566, 2009