In this study, a reactive phosphorus-containing organoclay (RPC) was successfully prepared through the cationic exchange reaction of sodium montomorillonite clay with hexyltriphenylphosphonium bromide and surface modification by grafting it with glycidyloxypropyltrimethoxy silane. It is characterized using X-ray diffraction (XRD) and Fourier transform IR (FTIR) measurements. A series of novel epoxy/clay nanocomposites (ERPC) was then prepared with a selected epoxy resin and varying amounts of RPC. The results of XRD and TEM of the nanocomposites showed that the RPC particles were well dispersed in the epoxy matrix with a highly exfoliated structure due to the presence of the reactive epoxide group of RPC. The as-prepared epoxy/RPC nanocomposites (ERPC) were thermally stable up to 388 degrees C. Thermal stability was increased by increasing the RPC content as indicated by the corresponding activation energies (Ea) and the integral procedural decomposition temperatures (IPDT). Furthermore, the storage modulus in the glass state of the nanocomposites was dramatically increased with the increase in RPC content. In addition, the large increment of limiting oxygen index (LOI) which was I I units higher than that of the neat epoxy indicates that an extraordinary enhancement of flame retardancy was obtained from the nanocomposite containing 5 wt% of RPC. (C) 2008 Elsevier Ltd. All rights reserved.