The implantation with nitrogen ions accelerated at 150 kV has been performed on sheets of high purity iron (99.99%) annealed for 1.8 ks at 773 K and/or cold-rolled with 90% reduction. Dose of the ions was changed in the range of 8 × 10 18 to 4 × 10 20 N 2+/m 2. Hardness increased for a wide range in depth and its increments is large in the deformed specimen compared with the annealed and implanted specimen. Iron nitride, Fe 16N 2 (α″), is formed in both the deformed and the annealed specimens, and the size of α″ particle in the former is smaller than that in the latter. The formation of α″ in the deformed specimen is accompanied by the disappearance of dislocation substructures.