The influence of intermetallic Al-Mn particles on the corrosion behavior of in-situ formed Mg-Al layered double hydroxide (Mg-Al-CO₃^2--LDH) steam coating on AZ31 Mg alloy was investigated. The alloy was pretreated with H₃PO₄, HCl, HNO₃ or citric acid (CA), followed by hydrothermal treatment, for the fabrication of Mg-Al-LDH coating. The microstructure, composition and corrosion resistance of the coated samples were investigated. The results showed that the surface area fraction of Al-Mn phase exposed on the surface of the alloy was significantly increased after CA pretreatment, which promotes the growth of the Mg-Al-LDH steam coating. Further, the LDH-coated alloy pretreated with CA possessed the most compact surface and the maximum coating thickness among all the coatings. The corrosion current density of the coated alloy was decreased by three orders of magnitude as compared to that of the bare alloy.