Yttria-stabilized zirconia is the most developed solid electrolyte for use in hightemperature solid oxide fuel cell (SOFC). Commercial yttria-stabilized zirconia powders reach high densification at temperatures around 1400 °C. The use of additives may increase the densification rate by means of a liquid phase formation during sintering. However, these additives should not cause any degradation on the ionic conductivity of the electrolyte. The main purpose of this work was to study the effect of Co addition on the densification and electrical conductivity of yttriastabilized zirconia. Green compacts were prepared by pressureless sintering a mixture of commercial 8 mol% yttria-stabilized zirconia with cobalt carbonate. Linear shrinkage results show that the temperature at which the shrinkage starts decreases with increasing Co content. Impedance spectroscopy measurements reveal that Co additions to stabilized zirconia decrease the total electrolyte conductivity even for Co contents as low as 0.05 mol%.