The saturation magnetization Is' magneto‐elastic parameter η, coercive force He' and domain structure have been investigated in Fe–Ni films. It is shown that changes in phase composition cause the abrupt alterations in magnetic properties of the films; e.g., for films 20% Ni–80% Fe Is falls by ≈ 1.5 times during α → γ transformation, and η rises by ≈ 1.6 times. A considerable increase in Hc is observed; its character depends on film thickness.