Four different Au/Al2O3 catalysts were prepared via impregnation and deposition precipitation. The preparation technique used was found to have a large influence on the average Au particle size and amounts of Au adsorbed. For CH4 oxidation a clear particle size effect was observed, in which small Au particles are beneficial for high activity. From the preparation methods studied, homogeneous deposition precipitation leads to the smallest average particle size (3-5 nm) and, hence, to the most active catalysts. These catalysts, however, showed some sintering of Au accompanied by a slight deactivation during catalytic reaction. The results do not support the idea of ionic Au being responsible for the catalytic activity.