The viscoelasticity of epoxy resin/silica hybrid materials manufactured by the sol-gel process with an acid anhydride curing agent was investigated in terms of morphology. Transmission microscopy observations demonstrated that all the prepared hybrid samples had a two-phased structure consisting of an epoxy phase and a silica phase. The formed silica had either nanosized particles or coarse domains, depending on the catalyst for the sol-gel process. Raman spectroscopy analysis showed that the formed silica had features typical of sol-gel derived silica glass and that the ring-opening reactions of the epoxy groups developed in the hybrid samples and in the neat epoxy samples. In dynamic mechanical thermal analysis, there were two transition temperatures due to epoxy chain mobility and epoxy network relaxation, through which the moduli changed by nearly 3 orders of magnitude. The hybridization disturbed epoxy network formation but also reinforced the epoxy network with the formed silica, which was characterized by the activation energy of the network relaxation; therefore, the modulus of the rubbery state was correlated to the activation energy. (C) 2008 Wiley Periodicals, Inc.