Abstract: The growth technology of LPE is studied for the films of Bismuth substituted iron garnets. At the wavelengths between 0.40μm and 0.80μm,the saturated Faraday rotation spectrum and optical absorption spectrum have been obtained at room temperature for (Bi, Y, Lu)₃(Fe, Ga)₅O₁₂ LPE films with different Bismuth contents. Results indicate that in the vicinity of wavelength 0.5μm, there are the peaks of the rate of the specific Faraday rotation θ_F and optical absorption coefficient α, thus proving the existence of a strong magnetooptic active transition in this region. The microscopic causes of the transition are discussed.