The replacement of Co by Nb in the La1-xBaxCo1-yNbyO3-delta (0.6 <= x <= 1.0) system and its effects on phase stability and high temperature properties of the cubic perovskite phase were investigated by X-ray diffraction, dilatometry, electrical conductivity, oxygen permeation and electrochemical impedance spectroscopy. The incorporation of Nb in the B site stabilizes the cubic perovskite in the as prepared samples. The Nb solubility increases from y = 0.1, for the sample with Ba content x = 0.6, to y = 0.4 for 0.8 <= x <= 1.0. However, after a heat treatment at 750 degrees C during 10 days small amounts of secondary phases were detected for samples with x = 0.9 and 1.0. The linear expansion of the cubic phases decreases with the Nb content as well as with the Ba content. The minimum value, alpha = 12.9 x 10(-6) K-1, was obtained for La(0.2)Ba(0.8)Co(0.6)Nh(0.4)O(3-delta). The behavior of electrical conductivity and oxygen permeation data with Nb content is explained from variations in the oxygen vacancy concentration, which is controlled by Nb2+ and Ba2+ contents. The minimum polarization resistance value, Rp = 0.08 Omega cm(2), was obtained at 600 degrees C for La(0.2)Ba(0.8)Co(0.6)Nh(0.4)O(3-delta). The low Rp value of this compound and the crystal structure stability of various compositions in the system La1-xBaxCo1-yNbyO3-delta with x >= 0.7 and y >= 0.1 make these materials of interest as mixed conductors. (C) 2016 Elsevier B.V. All rights reserved.