Isotopically enriched iron (56Fe or 57Fe) films were deposited on Si(100) substrates at RT by a low-energy (50–500 eV), mass-separated ion beam deposition (IBD) method. All the IBD-Fe films had smooth and fine-grained polycrystalline bcc-structure, and showed superior electrochemical corrosion resistance against both NaCl and H2SO4 solutions compared with die highest-purity (RRRIH=6000) iron metals ever reported. A distinct energy dependence of the degree of corrosion resistance and different microcrystalline structures observed by TEM cross-sections for the 50 eV- and 100 eV-IBD-Fe films indicate that their film growth modes are completely different.