Au/Al2O3, NiO x /Al2O3, and (Au + NiO x )/Al2O3 composites have been prepared by ion exchange and impregnation. Their structural and electronic properties, including the size and shape of supported metal particles and the oxidation state and ligand environment of the Au and Ni atoms, have been investigated. The catalytic action of Au/Al2O3, NiO x /Al2O3, and (Au + NiO x )/Al2O3 in the water-gas shift reaction and carbon monoxide oxidation is reported. At 300–450°C, the CO conversion over (Au + NiO x )/Al2O3 exceeds the sum of the CO conversions over the monometallic catalysts Au/Al2O3 and NiO x /Al2O3 by a factor of 2–3. An explanation is suggested for the nonadditive increase in the CO conversion over the Au-Ni catalysts.