The dielectric functions of in-situ crystallize BZT thin films fabricated on Pt(111)-coated Si wafers by multi-target reactive sputtering (MTRS) were obtained by means of spectroscopic ellipsometry in the spectral range from 0.8 to 8.7 eV. Investigation of the optical data of BaZr0.2Ti0.8O3 above 4 eV was performed for the first time and the interband transition energy of the O 2p to Zr 4d transition was derived to be ~7.7 eV.