Pr2NiO4-based oxides were studied as a series of new mixed electronic and oxide-ionic conductors for oxygen permeation membrane. High electronic conductivity was observed for the Pr2NiO4 system and the temperature dependence was of metal-like behavior, i.e., it decreased with elevating temperature. The oxygen permeability of Pr2NiO4-based oxides was much higher than that of La2NiO4-based oxides with the same K2NiF4-type structure. The effects of the Ni-site dopant were also studied and it was found that the oxygen permeation rate was improved by doping Cu and Mg. In particular, doping of Cu is most effective for enhancing the oxygen permeation rate from air to He, and the optimum concentration of Cu was found at 20%. The maximum permeability of 60 mu mol min(-1) cm(-2) at 1273 K was attained using a 0.5 mm thick Pr2Ni0.8Cu0.2O4 membrane. Addition of the excess Cu to Pr2Ni0.8Cu0.2O4 significantly enhanced the oxygen permeation rate, probably due to the remarkable grain growth assisted by the formation of some Cu-containing liquid phase, and the oxygen permeation rate reached to 100 mu mol min(-1) cm(-2) with the same conditions. (c) 2006 The Electrochemical Society.