Epoxy/silica composites have been used widely as the electronics packaging materials. This paper tested the thermal properties, moisture absorption and dielectric properties of pure epoxy and epoxy composites with micron-sized silica and nano-sized silica. The master curve of the dielectric loss factor was obtained by time-temperature superposition principle. Results showed that the nano-composite had a much higher loss factor, lower glass transition temperature and higher moisture absorption than other samples. By the analysis of the origin of the dielectric response in epoxy/silica composite, the reason for the different dielectric relaxation behaviors of the nano-composite, the microncomposite, and the pure epoxy was discussed. (c) 2005 Published by Elsevier Ltd.