A systematic study of the relationship between microstructure, composition and conductivity of zirconia-alumina composites grown from the melt are reported in this article. Directionally solidified ZrO2 (3 mol%Y2O3)-Al2O3 composites have been prepared with eutectic composition and enriched in zirconia. Growth conditions have been chosen to achieve homogeneous microstructures as much as possible. The shortest dimension of the zirconia particles ranged from 1 mu m to below 80 nm. The total conductivity of these specimens has been measured indicating that the density of the Al2O3-ZrO2 interphases is not relevant to the conductivity. The conductivity increases only slightly with growth rate and is somewhat larger than the conductivity expected for a homogeneous dispersion of spherical zirconia particles on insulating Al2O3, due to the preferential alignment along the growth direction. The conductivity in the eutectics (33.5 vol.% zirconia) is 1.2 x 10(-3) ohm(-1) cm(-1) at 800 degrees C and can be increased 2.8 times in composites with + 12 vol.% excess zirconia when the growth conditions achieve the favorable microstructure. (c) 2007 Elsevier B.V. All rights reserved.