Yttria-stabilised zirconia (YSZ) electrolyte films for solid oxide fuel cell (SOFC) applications have been prepared by reactive DC sputtering. The pore structure of the anode substrates was modified by sintering at different temperatures between 1300 and 1400 degreesC and the influence of this microstructure on the gastightness of the deposited films was studied. The characterisation of the microstructure includes measurements of electrical conductivity as well as determination of porosity by image analysis and mercury porosimetry. At sintering temperatures of 1380 and 1400 degreesC, the surface of the anode substrate, coated by an anode functional layer, was dense. The 5- to 8-mum-thick sputtered electrolyte films were annealed again to increase the gastightness. At an annealing temperature of 1360 degreesC, a He leakage rate of 8 x 10(-8) mbar l/cm(2) s was achieved. (C) 2003 Elsevier Science B.V All rights reserved.