Mixed conductivity and oxygen permeation property in Pr2Ni0.75Cu0.25Ga0.05O4 were investigated. After examining various Ga concentrations, it was found that cation excess composition of Pr2M0.75Cu0.25Ga0.05O4 achieved the highest oxygen permeability of 298 mu mol-min(-1) cm(-2) (6.68cc.min(-1).cm(-2)) at 1273 K from air to He with a 0.5 mm thickness. The oxygen permeability of Pr2Ni0.75Cu0.25Ga0.05O4 increased with increasing the activity of surface catalyst and the highest permeation was achieved when La0.9Sr0.1Co0.8Fe0.2O3 was used for the surface catalyst. The oxygen nonstoichiometry was further studied by using thermogravimetry. It was confirmed that the excess amount of oxygen was introduced at high P-O2 range, which might be the origin of the high oxygen permeation rate in this oxide. (c) 2007 Elsevier B.V. All rights reserved.