The protective performances of coatings formed by organo-silanes with a long alkyl chain for AZ31 magnesium alloy corrosion protection were evaluated by electrochemical techniques. The coatings were formed in hydroalcoholic baths of octyl- or octadecyl-trimethoxy-silane, and hydrolyzed at different pH values. The coatings formed at all the pH by the lower homologue were always porous and scarcely protective. Those built by the higher homologue were more corrosion resistant and the best results were observed when octadecyl-trimethoxy-silane was hydrolyzed at pH 5: in this case a thick, scarcely defective, layer was formed and no evident corrosion attack was observed after 1000 h immersion in 0.05 M Na2SO4 solution. (C) 2008 Elsevier B.V. All rights reserved.