Cyanate ester (CE)/bentonite (BT) nanocomposites were prepared by melt blending of CE with NH4+-BT. The nanostructure of CE/BT nanocomposites was studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was found that partially intercalated and partially exfoliated structures coexisted in CE/BT nanocomposites containing 2.5 wt % BT with respect to that of bulk CE. Below 2.5 wt % BT content, a totally exfoliated and disordered structure was formed in the nanocomposites. The exfoliated BT enhanced the toughness of CE/BT nanocomposites. The impact strength showed a maximum of 7.1 kJ/m(2) at 1 wt % BT, compared to 3.8 kJ/m(2) of pure CE. Furthermore, results of thermogravimetric analysis (TGA) suggest that CE/BT nanocomposites have higher thermal stability. (c) 2005 Wiley Periodicals, Inc.