MgAl-LDH films were produced through hydrothermally chemical conversion of pre-prepared anodic films on Mg alloy AZ31. The growth behavior and corrosion performance of the LDH films were investigated. Results reveal that morphology, chemical compositions and structure of LDH films vary greatly as a function of the conversion treatment conditions. Internal sources of Mg2+ and Al3+ cations for the formation of LDH films were ascribed to: (i) degradation of the anodic films; and (ii) dissolution of the AZ31 substrate. Moreover, the Stranski-Krastanov (SK) growth mode, two-dimensional layer growth (2D) to three-dimensional (3D) growth, was proposed to explain the transformation process.