The effect of alumina content on the electrical and thermal properties of substrates consisting of tetragonal zirconia polycrystals and various volume fractions of Al₂O₃ was studied. The substrates were fabricated by the doctorblade casting, using an Al₂O₃ powder and coprecipitated zirconia powders with compositions 4 mol% YO_1.5-4mol%CeO₂-ZrO₂ and 3mol%Y₂O₃-ZrO₂, and their surface roughness and microstructure were investigated. The average surface roughness (R_a) of the substrates was smaller than 0.1μm. The dielectric constant (ε), dielectric loss tangent (tanδ) and thermal expansion coefficient of the substrates decreased with increasing alumina content. The volume resistivity of the substrates was not sensitive to the alumina content in the range of 33.9 to 69.8vol%. It depended on the volume resistivity of TZP.