Epoxy-clay nanocomposites were synthesized using two organoclays cured with different chemicals at different temperatures. Interlayer distance of the clay layers and curing process were investigated by X-ray diffraction and infrared spectra. The clay treated with facilitated curing agent, 2,4,6-tris[(dimethylamino)methyl]phenol, can exfoliate at all curing conditions, but for the other clay treated with low-speed curing agent, p,p'-diaminodiphenylmethane, exfoliation of the clay layers does not occur. It was found that the relative curing speed between the interlayer and extralayer was the most important factor determining clay exfoliation. Exfoliated epoxy-clay nanocomposites can be prepared if the curing speed of the interlayer is higher than that of the extralayer, irrespective of the curing agent and temperature used. (C) 2003 Wiley Periodicals, Inc.