The electrical properties and morphology of polycrystalline gold films prepared on alumina and silica substrates and epitaxial thin gold films deposited on mica are examined as a function of film thickness, substrate, structure and mercury adsorption. The resistivities were examined for these films and compared with an ideal, specular gold film in accordance with the Fuchs-Sondheimer (FS) model. According to the FS model, specular films should demonstrate optimum response to adsorbates which produce diffuse rather than specular conduction electron scatter. When the as-prepared polycrystalline films were exposed to mercury, the resistance increased for both the gold-alumina and gold-silica films, and it was found that the gold-alumina films had the greatest response and showed a pronounced thickness dependence. This is due to a rougher, more porous film produced on the polycrystalline alumina substrate which promotes diffusion of the mercury into the films’ grain boundaries and the gold bulk. When the epitaxial gold films were exposed to mercury, the resistivity oscillated with increasing mercury coverage. This may be attributed to the formation of successive monolayer coverage, and a resulting oscillatory change in specularity.