In this study, the oxygen non-stoichiometry in La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) under uniaxial compressive stress up to 77 MPa was investigated by means of coulometric titration. The oxygen deficiency determined by the transient current was almost constant under compression, whereas both cell resistance and relaxation time significantly increased and these two parameters showed good correlation. Their increase appears to be related to the oxidation process on the surface of LSCF decelerated by the contact pressure, whereas the compressive stress had little effect on the oxygen deficiency in LSCF. Creep deformation was found to have limited effect on oxygen deficiency. Experimental observation also demonstrated that chemical expansion could cause unexpected internal stress, which would not change the oxygen deficiency. (C) 2017 Elsevier Ltd. All rights reserved.