The effect of the structural phase transition on the electrical and electrochemical properties of GdBaCo2O5+x has been analysed in order to evaluate its suitability as an electrode material for high-temperature applications, in particular as a cathode for Solid Oxide Fuel Cells (SOFCs). X-ray diffraction evolution with the temperature and differential scanning calorimetry were used to determine Structural features of the phase transition, e.g. phases symmetry, thermal expansion coefficients, transition temperatures and enthalpy changes. Four-probe dc-electrical measurements of dense pellets of GdBaCo2O5+x and electrochemical characterization by means of impedance spectroscopy as a part of a symmetrical cell (GdBaCo2O5+x/La0.9Sr0.1Ga0.8Mg0.2O3-delta/GdBaCo2O5+x) were carried out yielding high stability of this material across the mentioned phase transition. The thermal relation of the oxygen stoichiometry with the structural and electrical features revealed the importance of the oxygenation/deoxygenation processes taking place in this material. (c) 2008 Elsevier B.V. All rights reserved.