In order to apply for magneto-optical (MO) devices, the thermally non-equilibrium Bi₃Fe₅O₁₂ (BIG) films have been investigated. The films were prepared by metal organic decomposition (MOD) technique. The BIG thick film prepared in our previous processing showed the low Faraday rotation which was the same performance of the film with 300 nm. According to our previous preparation process, the crystallization from the amorphous phase to the garnet phase by post annealing was achieved after final spin-coating. We modified the process and repeated the post annealing process after every 5 times coating, then we obtained the thick film with high MO performance. The XRD analysis showed cube on cube crystal growth of the film on the substrate. The Faraday rotation of the film increased in proportion to the thickness of the film. The saturation magnetization was approximately 150 mT. The ferromagnetic resonance indicated the in-plane magnetic anisotropy. The microstructure of the cross section of the film revealed some damage at the interface area between the film and the substrate, which suggests more improvement of the annealing process. However, the BIG thick film prepared by MOD technique has high MO performance for the application for the optical devices.