The influence of the montmorillonite type and concentration on the mechanical properties and morphology of a carboxyl-terminated butadiene acrylonitrile toughened epoxy/montmorillonite nanocomposite has been studied. Modified montmorillonite can be well dispersed in a carboxyl-terminated butadiene acrylonitrile toughened epoxy/montmorillonite nanocomposite. Jeffamine, a curing agent, contributes to the intercalation of sodium montmorillonite, allowing the loss of the ordered layered structure in the nanocomposite. The preparation method of the nanocomposite has a slight effect on the mechanical properties. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 685-692, 2009