In this work, the synthesis of polypropylene (PP)/ graphene nanosheet (GNS) nanocomposites by in situ poly-merization using metallocene catalysts was studied. Initial reactions were performed using rac-Et(Ind) 2 ZrCl 2 and rac-Me 2 Si(Ind) 2 ZrCl 2 catalysts to select the best one to obtain good molecular weight, thermal properties, and tacticity. Subse-quently, PP nanocomposites with different loadings of GNS were obtained. GNS from two different sources [Graphite Nacional (GN) and Graphite Aldrich (GA)] have been used, and the differences between the obtained nanocomposites were evaluated. The GNS and nanocomposites were studied by scanning electronic microcopy, transmission electronic micro-copy, and X-ray diffraction. They showed that the GN nano-sheets had lower crystal size and diameter than the GA nanosheets and dispersed better in the PP matrix. Differential scanning calorimetry analyses of both types of nanocompo-sites showed an increase in the crystallization temperature with increasing graphite loading. The polymeric materials were also characterized by GPC, thermogravimetric analysis, and 13 C NMR. V C 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 3598–3605, 2012