A novel aromatic amine organo-modifier synthesized in our previous work was used to treat montmorillonite (MMT) and the organo-modified MMT was used to prepare poly(etherimide) (PEI)/MMT nanocomposites by a melt intercalation method. MMT treated by this amine exhibited large layer-to-layer spacing and a high ion-exchange ratio (>95%). The nanocomposites were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic mechanical analysis, a universal tester, thermogravimetric analysis, and by differential scanning calorimetry. The results of XRD and TEM showed that the nanocomposites formed exfoliated structures even when the MMT content was 10 wt %. When the MMT content was below 3 wt %, the PEI/MMT nanocomposites were strengthened and toughened at the same time. The nanocomposites also showed marked decreases in coefficient of thermal expansion and solvent uptake. (C) 2003 Wiley Periodicals, Inc.