In this work, diglycidyl ether of bisphenol A (DGEBA) epoxy resin was cured by isophorone diamine (IPD) hardener in the presence of amine-functionalized silica nanoparticles. Depending upon the aminated silica (AS) contents, two epoxy networks labeled by EP/AS-2.5 and EP/AS-5.0 were obtained. The amine functional groups can allow the nanoparticles to be covalently incorporated into the epoxy matrix. Two controls, including epoxy network loaded by pristine silica (EP/S-2.5) as well as neat epoxy network, were also prepared via a similar protocol. Thus, thermal and mechanical behaviors of the resulting materials were studied as a function of silica surface characteristics, i.e., hydrophilic vs. organo-modified surface, and its loading content. The initial decomposition temperatures (T (IDT)) and the temperatures of the maximum decomposition rate (T (max)) were improved. The AS nanoparticles could enhance the storage moduli (E' values) of the epoxy networks at high-temperature region. Dynamic mechanical analyses also showed that the amine-functionalization of silica can lead to a superior interaction between the nanoparticles and the resulting DGEBA/IPD epoxy networks.