Slip casting is a significant method and it is widely used in ceramic manufacturing. In order to investigate the influence of water processing in slurry fabrication on microstructure and oxygen permeation of Ba1.0Co0.7Fe0.2Nb0.1O3-delta (BCFN) membrane, disk-shaped membranes are made from powders with/without water processing and these membranes are checked by XRD, SEM and oxygen permeation measurement. We find barium of material dissolves into water during slurry fabrication through ICP-OES method and the A-site stoichiometric ratio is 0.986 because of the water processing, and the oxygen permeation flux of water-treated membrane is 25.2% lower than that of original membrane after sintered at 1110 degrees C. With the increase of sintering temperature, the oxygen permeation of water-treated membrane almost recovers and is only 7% lower than the original membrane while sintered at 1150 degrees C. A composition segregation and homogenization mechanism is proposed through microstructure and properties analysis. (C) 2012 Elsevier B.V. All rights reserved.