Au/gamma-Al2O3 catalysts were prepared by depositing AuCl3 onto low-soda gamma-Al2O3 under different pH. EXAFS (extended X-ray absorption fine structure) analysis showed that Au species were mainly in the Au-O bonding environment when dried at 298 K, regardless of the suspension pH during deposition. Au-(O)-Al bonding was also suggested from EXAFS analysis of catalysts prepared at pH ranging from 4.1 to 9.4, indicating a deposition via the coordination of surface hydroxyl groups to Au species. However, Au-(O)-Au was found instead of Au-(O)-Al in the catalyst prepared at an extreme pH of 10.5, indicating a deposition of polymeric Au(OH)(3). The catalysts were tested for CO oxidation without further pretreatment. The one prepared at pH 10.5 catalyzed the CO oxidation reaction effectively at 323 K whereas that prepared at pH 4.1 showed negligible activity. This suggested that a specific Au-O morphology, such as the polymeric Au(OH)(3), could be responsible for the high CO oxidation activity of supported Au catalysts.