Abstract: Nanocomposites are formed by contacting a nanoclay with an onium ion surface treatment agent and an anhydride-curable epoxy resin. The onium ion agent converts the interlayer region of the nanoclay from hydrophilic to hydrophobic. The anhydride-curable epoxy resin can be easily intercalated into the interlayer spacing. The co-presence of the anhydride-curable epoxy resin in the interlayer space provides surprising increase in glass transition temperature for anhydride-curable epoxy resin nanocomposites in addition to enhanced mechanical, thermal and chemical resistance properties.