A series of Au/MgO2-TiO2 with various Mg/Ti molar ratios was prepared to study its catalytic activity for preferential oxidation of carbon monoxide in hydrogen-rich stream (PROX). An incipient wetness impregnation method was used to prepare the MgOx-TiO2 support, using aqueous solutions of Mg(NO3)(2) on TiO2 calcined at 300 degrees C. A deposition-precipitation (DP) method was utilized to prepare Au/MgOx-TiO2, using HAuCl4 as the starting material. Au/MgOx and Au/TiO2 were also included for comparison. Investigation was carried out to study the effect of Mg/Ti molar ratio on the catalytic properties of gold supported catalysts. The catalysts were characterized by inductively couple plasma-mass spectrometry, X-ray diffraction, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy. TEM results revealed the presence of nanosized gold particles and narrow particle size distribution on all the catalysts. MgOx was deposited on the TiO2 surface in the form of thin islands without definite shape. MgOx was mainly present as Mg(OH)(2). Au particles were deposited on the surface of TiO2 in intimate contact with MgOx. The gold particle size was around 2.5 nm and was smaller than the MgOx particles. Since the surface area of TiO2 was small and the MgOx concentration was comparatively higher than An concentration, Au should be in intimate contact with MgOx on the TiO2 surface. However, the exact status depends upon the Mg/Ti ratio and pH value during DP process to deposit gold. Au/MgOx-TiO2 with suitable amount of MgOx has higher CO conversion and higher selectivity Of O-2 to CO oxidation in the PROX reaction than Au/MgO and Au/TiO2.