Oxygen-permeation measurements were carried out on a Gd0.85Ca0.15AlO3-delta specimen in the temperature range of 400-900 degrees C as a function of the oxygen partial pressure from 1.01 x 10(5) to 18.85 Pa. Simultaneously, the open-circuit voltage of the permeation cell and the voltage upon partially short-circuiting the cell over external resistances were measured. As a result, the ionic conductivity of Gd0.85Ca0.15AlO3-delta between 650 and 900 degrees C and the electronic conduction parameter p(circle plus) of the hole conductivity were obtained as a function of temperature. The electrochemical performance as well as the stability of the electrolyte material were studied by carrying out cell-voltage measurements under Ar + 1000 ppm H-2 (anode) and air (cathode) environments. The present investigations suggest that Gd0.85Ca0.15AlO3-delta is predominantly an oxygen-ion conductor with an ionic conductivity slightly below that of yttria-stabilized zirconia. (C) 2008 The Electrochemical Society.