Effects of alumina addition on ionic conductivity for alumina/8YSZ composite was examined in which conductivity shows a slight increase with alumina addition. The alumina addition has a role in increasing the 8YSZ/8YSZ interface (grain boundary) by suppressing the matrix grain growth as well as increasing the population of the alumina/8YSZ interface. The increase in ionic conductivity in composite was suggested not to be ascribed to the alumina/8YSZ interface but to the grain boundary.