It has been known that an ion-beam-assisted deposition (IBAD) process can produce thin films with different physical properties by changing conditions of assist-ion-beam. The aim of this study is to produce Fe thin films by the IBAD and an ion-beam-sputter deposition (IBSD) process which uses no assist-ion-beam and then to examine relationship between the microstructure and the corrosion resistance of the films. Five types of the films were prepared using the IBSD and the IBAD with various conditions of assist-ion-beam. The corrosion resistance of the films prepared was examined in 0.1 kmol·m-3 Na2SO4. The micro-structure of the films was observed by transmission electron microscope (TEM) and the surface topography of them was measured by atomic force microscope (AFM). All the films were consisted of α-Fe microcrystals. The grain size of the IBAD films was half of that of the IBSD films. The corrosion tests in 0.1 kmol·m-3 Na2SO4, exhibited that corrosion pits on the IBAD films initiated immediately but those on the IBSD films occurred at about 5 ks after immersion. The number of the pits on both the films increased for a short time and became constant after a given time. The increase rate of pit radius on the IBAD films was larger than that on the IBSD films. According to the observation by AFM, the surface of the IBAD films was roughened by the irradiation of assist-ion-beam. The roughness of the films with low corrosion resistance was larger than that with high corrosion resistance. The corrosion resistance of the IBAD films was influenced by Ar flow rate in the hollow cathode compared with assist-beam-voltage.