Bi-substituted gaet films with perpendicular anisotropy have been prepared by a sol-gel method. Annealing effects on magneto-optical properties and structures of the films are studied. The results indicate that the Kerr hysteresis loops of gaet films have good squareness at annealing temperatures above 650℃ , the coercive force Hc of these films increases from 1070 to 1570 Oe with the increasing temperature from 650℃ to 700℃. The Kerr rotation of the films was changed with the increasing annealing temperature, and there is a maximum value (0.82°) at 675℃ . It was found that the structure of the films is a single phase of gaet without preferring orientation when the annealing temperature is about 650℃ , but a new phase (Bi2 Al4O9) can be formed when the annealing temperature reaches 675℃, another new phase (Bi2Fe4O9) appears when the annealing temperature is about 700℃.