A new graphite/polystyrene composite was produced with cationic grafting polymerization of styrene initiated by CO+ClO4- group on the surface of expanded graphite (EG). The structures of EG and the graphite/polystyrene composite were studied with SEM and optical micrograph. The spectra of XRD and IR were used not only for confirming whether the polymerization reaction took place, but also for determining whether the polystyrene in the composite covered the surface of EG particles or intercalated into EG particles. The electrical conductivity, thermal phase transitions and mechanical properties were also discussed. (C) 2004 Published by Elsevier Ltd.