Multiferroic BiFeO3 thin films were prepared on Pt/TiO2/SiO2/Si and ITO/glass substrates by sol–gel preparation method. Pure perovskite phase and uniform surface topography have been verified by X-ray diffraction and atomic force microscopy, respectively. In addition, optical property measured by spectroscopic ellipsometer indicated that the absorptivity of both BiFeO3 thin films was enhanced with increasing photo energy after an illumination among 250–1000nm. Tauc calculation indicated that the direct band gap was 2.92eV for the film on Pt/TiO2/SiO2/Si, which is about 0.4eV lower than that of the film on ITO/glass.