In this work, we present our study on evaluating electro-optic properties of Ba0.7Sr0.3TiO3 thin films by prism coupling technique. Ferroelectric Ba0.7Sr0.3TiO3 thin films were epitaxially deposited on LaNiO3 electroded MgO (001) single-crystal substrates using pulsed laser deposition. Refractive indices and thickness of the Ba0.7Sr0.3TiO3 thin film were determined with a rutile prism (Metricon 200-P-2) under zero electric field at a wavelength of 632.8 nm. The angular shift of guided mode was observed subsequently with a conductive prism (Metricon 200-P-4aC) when electric field was applied to the thin film sample. The ordinary refractive index n(o) changes 2.2% under a dc voltage of 4 V (E similar to 11 V/mu m). The linear electro-optic coefficient tensor r(13) is thus calculated to be about 780 pm/V, showing the excellent potential of Ba0.7Sr0.3TiO3 thin films for use in active optical devices. (C) 2010 Elsevier B.V. All rights reserved.