A new method of surface modification which is effective in stabilizing silica grades of MCM-41 in the presence of water vapor is presented. It is shown by means of XRD, low-temperature nitrogen adsorption, and water vapor adsorption measurements that deposition of carbon from benzene Gaper pyrolysis considerably improves the stability and, furthermore, that this is achieved with only a small decrease of the pore volume and pore width in relation to those of the unmodified material.