Abstract We report the epitaxial growth of iron oxide overlayers on a platinum (111) single crystal, in the monolayer and the multilayer regimes. Different LEED structures have been observed for each of these regimes. At one monolayer coverage iron oxide forms an incommensurate overlayer with 10% longer unit cell vectors than those of clean platinum. At coverages of 3 to 10 monolayers, iron oxide forms a new structure, which is (2×2) with respect to that formed at one monolayer. AES and XPS show that the iron in the oxide overlayer is in the 2+ oxidation state and from ISS studies it was determined that both iron and oxygen are present in the outermost atomic layer in about equal amounts. Water adsorption on the iron oxide films was studied by TPD. It was found that the desorption spectrum is very sensitive to the presence of various types of defects on the oxide.