In the presence of an external magnetic field,doped perovskite oxides materials exhibit their metallic property due to the colossal magnetoresistance (CMR) effect,which can provide a negative permittivity at GHz frequencies.These materials are also known as ferromagnetic materials,which can provide a negative permeability in a frequency region near the ferromagnetic resonance (FMR).To date,there is no theoretical report on negative refraction properties of such anisotropic magnetic materials under ferromagnetic resonance conditions in detail.An analytic calculation of the initial complex permeability frequency spectra of thin film with in plane anisotropy,using Landau-Lifshitz-Gilbert theory,was presented.