Organo-acid-activated clays were prepared with different Surfactant contents by reaction of hexadecyltrimethylammonium hydroxide Solution and acid-activated clays. The intercalated cations adopted different orientation in the interlayer spacing of the acid-activated clays and their thermal stability depended on the Up taken amounts, acidity of the clay sheets and on the heating temperatures. The thermal stability of these materials was investigated using TG-MS, and followed by the in situ X-ray diffraction in nitrogen atmosphere. The clay sheets affected the decomposition of the surfactants, and as per consequence the thermal stability of the surfactants. TG-MS revealed that different types of water Molecules were detected during the heating process with additional CO2, alkanes and alkenes species at temperatures above 200 degrees C. The interlayer spacing collapsed after completed degradation of the intercalated surfactants. (C) 2009 Elsevier B.V. All rights reserved.