Single phase Ba and La co-doped BiFeO3 thin film was deposited on SrTiO3 (001) substrate by RF magnetron sputtering. Its optical properties were determined by analyzing the transmittance and ellipsometry spectra. A band gap of 2.65 eV was obtained. Additionally, the optical dielectric functions were changed by applying a varying magnetic field, which was attributed to the magnetoelectric coupling. (C) 2011 Elsevier B.V. All rights reserved.