Optical properties of amorphous Strontium Barium Niobate (a-SBN) thin films are investigated using spectroscopic ellipsometry. Since the SBN can be applied to optoelectronic devices, the dispersion of refractive index is desirable. The films are obtained by Pulsed Laser Deposition (PLD) onto MgO and Si substrates by targeting a SBN:60 monocrystal. The dielectric function of a-SBN is approximated using a single Tauc-Lorentz oscillator model. Thicknesses of the films and of their rough layer are in agreement with SEM and AFM results. The dispersion of the refractive index is presented in the 1 –5 eV range. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)