Gold catalysts, supported on a solid base of MgxAlO hydrotalcite, were prepared by a modified deposition precipitation method for CO selective oxidation. The preparation parameters and pretreatment of the catalysts were investigated. The pH and the HAuCl4 concentration in the initial solution, and the Mg/Al molar ratio of MgxAlO affected the pH in the final solution and determined the actual gold loading of the catalyst. The calcination temperatures of the MgxAlO support and the Au/MgxAlO catalyst dominated the Au3+/Au-0 ratio on the catalyst. The pretreatment of the catalyst as well as the gold loading and the Au3+/Au-0 ratio, critically determined the activity of the catalyst for CO selective oxidation. Based on XPS and in situ DR-FTIR analyses, a mechanism for CO selective oxidation on 2%Au/Mg2AlO was proposed. The hydroxyl group on Mg2AlO also participated in the reaction. (C) 2008 Elsevier B.V. All rights reserved.