Catalysts consisting of ultra-fine gold particles supported on iron oxide have been synthesized by the coprecipitation method. Subsequent to preparation, each sample was heat treated in air at four different temperatures, ranging from 473 K to 773 K. Steady state carbon monoxide oxidation was carried out over each sample. Upon extended reaction, catalyst deactivation took place over three of the catalysts whose respective surface compositions (e.g., gold to iron atomic ratio) were altered appreciably from their initial state. Surface structure analyses performed on all the unreacted catalysts have revealed variations in physical properties (e.g., degree of crystallinity and particle size). In addition, lattice parameters of gold were observed to increase up to 20 % from the bulk value. In contrast, XPS showed both gold and iron to be in essentially the same chemical states for all catalysts, irrespective of heat treatment temperatures. The importance of surface sensitive parameters to catalytic function are discussed.