A mixed conducting complex oxide La2Ni0.8Fe0.2O4+delta was prepared by complex sol-gel method. Ethylene diamine tetraacetic acid (EDTA) was used as the ligand. A dense supported membrane of La2Ni0.8Fe0.2O4+delta was fabricated by coating the sol on a porous alpha-Al2O3 substrate and followed by heat treatment. A single phase La2Ni0.8Fe0.2O4+delta membrane was obtained at 1123 K, which is much lower than the temperature needed for conventional solid state synthesis. The membrane is of no cracks detectable by gas chromatography. XRD verifies the presence of K2NiF4-type structure. delta is experimentally determined to be 0.17-0.22. The oxygen flux of the supported membrane, measured by steady state method, is not less than 1 ml cm(-2)min(-1) at 823 K, which is one order of magnitude higher than that of the supported membrane made from Fe-free La2NiO4+delta, showing its great potential for both air separation and catalytic membrane reactor applications. (C) 2003 Published by Elsevier Science B.V.