An Fe-Al thin film system was studied for the purpose of examining the formation and development of intermetallic phases, which were formed at the aluminum (Al) film-steel substrate interfaces. Al films having different initial thicknesses in the range of 2μ,14μm were deposited by physical vapor deposition and were then annealed at different temperatures (range: 300-650 °C) and for different time intervals (10 min-8 h). In order to explain the formation mechanisms of the intermetallics at the mentioned Al-Fe film interfaces, X-ray diffractograms (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) studies were used. The results showed that the intermetallic phases FeAl2 and Fe2Al5 were the most dominant phases that could be observed, and that they were formed sequentially, in contrast to intermetallics, which formed synchronously in bulk materials. © TÜBİTAK.