We incorporated organic modified layered silicates (OLS) into the mixture of epoxy and poly(ether imide) (PEI) to obtain a ternary hybrid nanocomposite and investigated its reaction-induced phase separation behavior. We found that OLS had dramatic impact to the phase separation process and the final phase morphology. The onset of phase separation and the gelation or vitrification time were greatly brought forward and the periodic distance of phase-separated structure was reduced when OLS was incorporated. Phase separation of the unfilled specimens was greatly suppressed at temperatures higher than 190 degrees C and no etch hole of PEI-rich phase could be observed in the SEM images. An interconnected, or bicontinuous morphology could only be observed at cure temperatures lower than 140 degrees C. On the contrary, the OLS-filled hybrid nanocomposites carried out obvious phase separation at cure temperatures ranging from 120 to 220 degrees C. Even at Cure temperatures higher than 190 degrees C, the hybrid nanocomposites had an interconnected phase-separated microstructure. These phenomena were related to the preferential wettability, chemical reaction of OLS with epoxy oligomer and the enhanced viscosity of the mixture. (c) 2005 Elsevier Ltd. All rights reserved.