Abstract At temperatures below the occurrence of thermal desorption of Ag atoms, the compositional and structural changes of Ag/Ir(111) films are investigated. From depth profiling measurements, we demonstrate that a small amount of silver atoms intermixes with iridium atoms in the interfacial layer to form a surface alloy. The three-dimensional rearrangement of iridium atoms by the ascending motion and dissociation at the steps provides an opportunity for silver adatoms incorporating into the Ir(111) surface. As the sample temperature increases for Ag/Ir(111), the logarithm of the intensity of the diffraction spot descends with an upswing around 450K as revealed using low-energy electron diffraction technique. This shows an enhanced structural ordering by thermally annealing for Ag/Ir(111) films. The morphological change of the Ag/Ir(111) system coincides with the increasing mobility in a three-dimensional configuration of iridium atoms.