Exfoliated nanocomposites based on polyamide 66 (PA66) and montmorillonite (MMT) were prepared and their thermal stability and combustion behaviour were investigated by using thermal gravity analysis and cone calorimeter. The nanocomposites exhibit higher thermal stability and good flame retardancy. The catalytic decomposition effect of MMT and the barrier effect of layer silicates are presented directly in isothermal oxidation experiment. The initial heat release rate plots show that the addition of MMT can accelerate the ignition of PA66 matrix. A ceramic-like char forms in the surface of the nanocomposites during burning. It is characterized by attenuated total reflection infrared spectra and scanning electron microscopy. (C) 2003 Elsevier Ltd. All rights reserved.