Cuprous oxide films, 25 to approximately 500Aå thick, formed on the (111) of copper were studied by x‐ray, electron microscopic, and ellipsometric techniques. The films were characterized in terms of their surface topography, epitaxial strains, mosaic spread, mosaic size, and their orientation relationships with the substrate metal. The films were demonstrated to contain large numbers of structural defects which could act as paths of easy diffusion, and a correlation was shown to exist between the rate of oxidation of the (111) of copper and the extent of these paths of easy diffusion in the oxide. Estimates were made of the effective grain‐boundary width and diffusion coefficient in , and it was concluded that substantial material transport could occur via these paths of easy diffusion.