Unsteady-state permeation in the initial stage was investigated on ceria-based dual-phase membranes by coating La0.6Sr0.4CoO3-delta (LSC) active porous layers onto the surface of membranes. It is found that the unsteady period is greatly influenced by the active porous layer. The membrane with LSC porous layers coated on both sides reaches a steady state immediately while starting the permeation testing. However, the membranes without LSC porous layers coated on one side or both sides need several to tens of hours to achieve the steady state. The active porous layer can improve the oxygen flux and decrease the permeation activation energy, and the membrane with coating on both sides had the highest flux and lowest E-a. In addition, the active porous layer can eliminate oxygen exchange limitations on the membrane surface. The changes of surface microstructures are suggested as the cause of unsteady-state permeation. (c) 2011 Elsevier B.V. All rights reserved.