Polypropylene/organoclay nanocomposites have been prepared via direct melt intercalation in an internal mixer. Maleic anhydride grafted polypropylene (PP-g-MA) was used as a compatibilizer to improve the dispersability of the clay. The structures of nanocomposites have been characterized by X-ray diffraction, transmission electron microscopy and rheometry in small amplitude oscillatory shear. The effects of concentration of PP-g-MA and processing parameters were investigated. Wide angle X-ray diffraction shows that the interlayer spacing, increases with the concentration of PP-g-MA, but is not significantly influenced by processing conditions. The study of linear viscoelastic properties shows that the storage modulus G' is very sensitive to the microstructure of the nanocomposite. A Carreau-Yasuda law with a yield stress is proposed to describe the rheological behavior of these materials. Applications to the twin screw extrusion process are also presented. (c) 2005 Elsevier Ltd. All rights reserved.