Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo-montmorillonite (O-MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The intercalation and exfoliation behavior of the epoxy nanocomposites were examined by X-ray diffraction and transmission electron microscopy. The curing behavior and thermal property were investigated by in situ Fourier transform infrared spectroscopy and DSC, respectively. The results showed that MMT could be highly intercalated by acidified CAB, and O-MMT could be easily dispersed in epoxy resin to form intercalated/exfoliated epoxy nanocomposites. When the O-MMT loading was lower than 8 phr (relative to 100 phr resin), exfoliated nanocomposites were achieved. The glass-transition temperatures (T-g's) of the exfoliated nanocomposite were 20 degreesC higher than that of the neat resin. At higher O-MMT loading, partial exfoliation was achieved, and those samples possessed moderately higher T-g's as compared with the neat resin. O-MMT showed an obviously catalytic nature toward the curing of epoxy resin. The curing rate of the epoxy compound increased with O-MMT loading. (C) 2004 Wiley Periodicals, Inc.