Environmental restrictions are leading to the research for environmentally friendly Cr-free treatments to substitute chromatizing. Recently, promising results have being reported for the corrosion protection offered by self-assembly monolayer (SAM) on different metals. In the present work, the influence of surface preparation on the electrochemical behaviour of SAM-treated At 5052 alloy in naturally aerated 0.5 M Na2SO4 solution (pH 4) has been investigated using EIS. The effects of three different surface treatments were compared: (A) alkaline cleaning; (B) alkaline cleaning followed by SAM treatment; (C) alkaline cleaning followed by acid etching and then SAM treatment. The results indicate that the acid-etching step, carried out after cleaning had a favourable effect on the corrosion behaviour of the Al 5052 alloy when it is subsequently treated with SAM process. (c) 2005 Elsevier Ltd. All rights reserved.