To investigate systematic relation between Ta doping and ion conductivity in (La, Sr)CoO3-delta, we have prepared La0.4Sr0.6Co1-xTaO3-delta(x = 0 - 0.2). The lattice volume was proportionally increased with increasing Ta content, suggesting that the Ta ions were successfully substituted into B-sites in the perovskite structure. The x-ray absorption fine structure spectra suggest that the Co ions were slightly reduced by doping Ta ions, meaning that the amount of Co4+ ions was decreased with substituting Ta4+ or Ta5+ into the B-sites. No variation of the Co-O distance was found for the Ta-substituted samples. Mean grain size was decreased with substituting Ta ions. Values of the oxygen permeation flux (OPF) and the ion conductivity a; were decreased with increasing Ta content, suggesting that the oxygen vacancy concentration decreases with Ta doping. The activation energies obtained by the OFF and the ion conductivity were increased with increasing Ta content. We suppose that the smaller grain size with Ta substitution is a reason for higher activation energy. (C) 2013 Elsevier B.V. All rights reserved.