The BaTiO<sub>3</sub> and Mn:BaTiO<sub>3</sub> thin films were fabricated on fused quartz and Si(111) substrates by a sol-gel method. The crystal structures of the samples were characterized by x-ray diffraction. It is shown that the samples are both polycrystalline thin films and possess cubic structure. The Mn-doping has no obvious effect on the crystal structure. The optical properties of the thin films were studied by transmitted spectrum technique or by spectroscopic ellipsometry depending on the substrate used. The transmitted spectrum shows that the absorption edge of the Mn-doping films has red shift compared with the undoping films. The energy gaps calculated from the transmitted spectrum are 3.68 and 3.39eV for undoping and Mn-doping samples, respectively. The results of spectroscopic ellipsometry shows that the refractive index of the Mn:BaTiO<sub>3</sub> thin film is bigger than that of the BaTiO<sub>3</sub> thin film. Which the change of energy gap and refractive index caused by Mn-doping can be explained by the Sellmeier Oscillator model.