The goal of this study is to determine the effect of the molecular structure of silane monomers on the corrosion protection properties of the formed silane layers. During the curing process, the silane monomers crosslink to form a molecular network, which acts as a barrier and retards the ingress of corrosive species. Non-cured and "fully" cured silane films with a comparable thickness were applied on cold rolled steel surfaces. The layer thickness and the chemical state of the films were measured with Spectroscopic Ellipsometry (SE). Electrochemical impedance spectroscopy (EIS) measurements and linear voltammetry clearly show that the number of silanol groups of the fully hydrolyzed silanes and the presence of an organo-functional group have a big influence on the barrier properties of silane layers and hence on their corrosion protection properties. (C) 2004 Elsevier Ltd. All rights reserved.