The present work consists in the study of the modification of a nano-layered vermiculite by thermal treatment up to 900 degrees C. Changes in the structure and texture after thermal treatment were used for evaluation of dehydration properties Of the Studied material. The dehydration properties of the clay are strongly affected by the crystal structure. The Differential Thermal Analysis (DTA) allows the determination of the specific temperatures at which phase modifications take place, principally the ones attributed to the removal of the interlayer water molecules and the formation of a series of less hydrated phases. Structural and textural Studies were carried out using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) analysis. The SEM micrographs reveal structural changes of the sample, such as exfoliation phenomena and contraction of the vermiculite, related to the heating temperature. These observations are confirmed by the XRD patterns, which demonstrate that the d-spacing of the first basal diffraction varies depending on the applied heating temperature, this showing several states of dehydration. As a complementary characterization. porosity analysis by Hg-porosimetry has also been carried Out. (C) 2008 Elsevier B.V. All rights reserved.