Ferromagnetic resonance in thin films has been extended to the radio‐frequency region of from 1–20 Mc. Theoretical expressions governing this resonance condition are given along with experimental results. It is found that resonance in this region affords an excellent means of measuring the anisotropy fieldHk. Films with compositions near 80% Fe—20% Ni were studied by this technique. The anisotropy field of these films was found to be around 5 oe. The width of the absorption line varied from 0.6 to 2.4 oe, depending on the composition of the film. The minimum linewidth was found to occur for the composition of minimum magnetostriction.