The oxygen evolution and reduction properties of La 0.8 Sr 0.2 CoO 3 are characterized using two-dimensional model electrodes with different reaction planes, synthesized on SrTiO 3 single crystal substrates by pulsed laser deposition. Thin-film X-ray diffraction and reflectivity measurements confirm the epitaxial growth of 29-nm-thick La 0.8 Sr 0.2 CoO 3 (001), (110), and (111) films on SrTiO 3 (001), (110), and (111) substrates, respectively. Cyclic voltammetry curves in 1-M KOH aqueous solution indicate that the (110) film has the highest activity for oxygen evolution and reduction reactions. An expansion of the La 0.8 Sr 0.2 CoO 3 lattice is observed after the oxygen reduction process, indicating the formation of oxygen defects, with the highest number of defects being produced in the (110) film. X-ray reflectivity analysis demonstrates the formation of a surface layer on the La 0.8 Sr 0.2 CoO 3 films during electrochemical cycling due to the decomposition of La 0.8 Sr 0.2 CoO 3 . The surface structure constructed at the electrode/electrolyte interface is a crucial factor influencing oxygen evolution and reduction activity of La 0.8 Sr 0.2 CoO 3 .