The electrical conductivity and microstructure of La0.65Sr0.3MnO3 (LSM)-8 mol% yttria-stabilized zirconia (YSZ) cathode composite were investigated from room temperature to 1000 degreesC in air conditions. The results show that dense YSZ, containing 7.52 +/- 0.15 mol% Y2O3 composes of equiaxed grains. Little glassy phase, consisted of SiO2 with minor Al2O3, is found in YSZ. Two conducting species are responsible for the conduction of YSZ in low and high temperature ranges. One is Y-Zr' V-O(..) with higher activation energy of 103 U mol(-1) below 550 degreesC and the other is V-O(..) with lower activation energy of 93 U mol(-1) above 550 degreesC. The transition temperature decreases from 550 to 400 degreesC for the composites with 10 or 20 vol.% LSM-YSZ. The LSM phase and YSZ dominates the electrical conductivity of composites below and above 400 degreesC, respectively. As the percolation limit is reached (20 vol.% LSM), the electrical conductivity of the composites is determined by LSM phase. The effect of secondary phases on electrical conductivity is insignificant even sintering at 1400 degreesC for 24 h. (C) 2003 Elsevier Science B.V. All rights reserved.