Mg(OH)(2) films have been fabricated on magnesium alloy AZ91 substrates by an in-situ hydrothermal method. AZ91 alloy substrates act as both the source of Mg2+ ion and the support for the Mg(OH)(2) film in synthetic process. The effect of pH value and hydrothermal treatment time on the morphologies and corrosion resisting properties of Mg(OH)(2) film is studied. The obtained Mg(OH)(2) films are uniform and compact. The adhesion between the films and the substrate is strong due to the in-situ growth process, which enhances their potential for practical applications. Potentiodynamic polarization measurements showed that the Mg(OH)(2) films obtained at pH 10, 3 h exhibits the highest increase in corrosion potential at -0.7097 V and lowest i(corr), which suggests that it is the best effective film in improving the corrosion resistance of AZ91in all obtained films. (C) 2013 Elsevier B.V. All rights reserved.