This paper reports the preparation of maleic anhydride-grafted polypropylene (PPgMA)/Polyhedral Oligomeric SilSesquioxanes (POSS) hybrids by POSS grafting during a one-step reactive blending process. The morphology of the hybrid was studied in details by means of electronic microscopy (SEM, TEM) as well as by X-ray diffraction, showing POSS dispersion at the nanoscale. The grafting yield, assessed through extraction of non-grafted POSS showed a high efficiency of the reactive blending process. Thermal, rheological and mechanical properties were studied for POSS-grafted PPgMA in comparison with a non-reactive PPgMA/POSS nanocomposite as a reference and showed advantages in terms of higher thermal stability and improved mechanical properties in the case of the grafting process with respect to simple melt blending. (C) 2008 Elsevier Ltd. All rights reserved.