La doped BiGaO3 (LxBGO) films were fabricated by the Sol-Gel method on the Pt/Ti/SiO2/Si substrates. X-ray diffraction analysis shows that the films are polycrystalline with an orthorhombic structure. The atomic force microscopy images of the LxBGO films suggest that the surface morphology is smooth. The optical properties of the samples were investigated by the spectroscopic ellipsometry in detail. The dielectric functions were extracted and in good agreement with the Adachi dispersion function. More one step, the optical band gap tends to increase with increasing La composition, which is consistent with the results of theoretical prediction. These results are helpful for the fabrication of Bi-based opto-electrical devices such as ultraviolet detectors.