Mesoporous silica thin films have been prepared through evaporation-induced self-assembly in the presence of non-ionic PEO-PPO-PEO surfactants. We investigated the effects of acid-base post-synthesis treatments on the structure of SBA-15 by immersing the samples into diluted HCl or HNO3 solutions at ambient temperature and by exposing them to NH3 atmosphere. The evolution of the 2D hexagonal structure was investigated by X-ray reflectivity (XR) before and after removing the surfactant from the silica matrix. XR curves analyzed were evaluated by the matrix technique to obtain the average electron density of the films, the wall thickness, the electron density of the walls. (c) 2005 Elsevier B.V. All rights reserved.