Composite electrodes were prepared by adding 40 wt % La0.8Sr0.2FeO3 (LSF) into porous yttria-stabilized zirconia (YSZ) and their performance was studied as a function of time and calcination temperature. X-ray diffraction (XRD) patterns of the LSF-YSZ composites indicated an expanded lattice parameter after calcination above 1523 K, suggesting that Zr reacted with the LSF to form a Zr-doped perovskite; but XRD provided no evidence for reaction between LSF and YSZ after calcination at 1373 K or after operation for 1000 h at 973 K and 700 h at 1073 K. A composite of 40 wt % La0.8Sr0.2Fe0.9Zr0.1O3 in YSZ showed reasonable performance at 973 K, with an area-specific resistance (ASR) of 0.22 Ω cm2. Based on symmetric-cell measurements, electrodes calcined at 1123 K showed an initial ASR of 0.13 Ω cm2 at 973 K but this increased linearly with time to 0.55 Ω cm2 after 2500 h at 973 K. However, the ASR depended strongly on current density, decreasing dramatically under both anodic and cathodic polarization. Electrodes calcined at 1373 K showed an ASR of 2.5 Ω cm2 at 973 K but this value also decreased dramatically under polarization. Scanning electron microcopy images demonstrate that aging at 973 K and calcination at 1373 K cause significant sintering of the LSF. It is therefore suggested that deactivation is caused by morphological changes, rather than solid-state reactions, with a dense layer of LSF forming over the YSZ substrate.