Perovskite oxides BaxCo0.7Fe0.2Nb0.1O3 - delta (BxCFN, x = 0.95-1.04) are synthesized by solid-state reaction method. The effect of A-site nonstoichiometry on the phase development, sinterability, electrical conductivity and oxygen permeability of sintered BxCFN are investigated. A-site deficiency reduces the cubic phase formation temperature and promotes the sintering process significantly. The electrical conductivity of BxCFN decreases but oxygen vacancy concentration increases with increasing A-site deficient level, suggesting that the charge compensation is completed via the creation of oxygen vacancies rather than the valence increase of B-site cations. A moderate A-site deficiency increases remarkably the oxygen permeation flux, while excessive A-site deficiency deteriorates the oxygen permeation process due to the occurrence of defect association between oxygen vacancies and other opposite charged defects. (C) 2009 Elsevier B.V. All rights reserved.