Polyaniline (PANI) grafted silica nanoparticles (PANI-SNs) had been prepared firstly by the in situ chemical oxidating of aniline with ammonium peroxodisulfate (APS) from the surfaces of the aminopropyl silica nanoparticles (APSNs) successfully with a dispersion polymerization method. A percentage of grafting (PG) of 205.2% and a grafting efficiency (GE) of 37.7% were achieved, calculated from the results of elemental analysis (EA). The chemical grafting of PANI was confirmed using FTIR and UV/Vis. The morphology of the polyaniline/silica nanocomposites (PANI/SN) and polyaniline grafted silica nanoparticles (PANI-SNs) were examined by SEM and TEM. The surface composition was determined by XPS and TGA were used for the characterization of the thermal stability of the PANI-SNs. (C) 2004 Elsevier B.V. All rights reserved.