A mixed-conducting complex oxide La2NiO4+delta was prepared by complex sol-gel method. Both ethylene diamine tetraacetic acid (EDTA) and citric acid (Cit) were used as ligands. A dense supported membrane of La2NiO4+delta was fabricated by coating the sol on a porous alpha-Al2O3 substrate and followed by heat treatment. A single-phase La2NiO4+delta membrane was obtained at 1123 K which is much lower than the temperature needed for conventional solid-state synthesis. The thickness of the membrane is about 40 mum measured by weight method, and there is no cracks detectable by gas chromatography. X-ray diffraction (XRD) and IR spectrometry verify the presence of K2NiF4-type structure. delta is experimentally determined to be 0.15-0.19. The oxygen flux of the supported membrane, measured by the steady-state method, is not less than 0.3 ml cm(-2) min(-1) at 923 K, which is significantly higher than that of the bulk membrane made from by particle sintering similar material, showing its great potential for the application in both air separation and catalytic membrane reactor. (C) 2003 Published by Elsevier B.V.