(ZrO2:8 mol% Y2O3)(1-x)-(MgO)(x) ceramic composites have been prepared in the 0 less than or equal to x less than or equal to 0.70 range by evaporation of a suspension of ZrO2:8 mol% Y2O3 in a solution of magnesium nitrate and ethanol followed by pressing and sintering. The samples were analyzed by X-ray diffraction and scanning electron microscopy. The electrical properties were studied by impedance spectroscopy and analyzed taking into account the contributions due to the different microstructural constituents of the specimens. The results show that the dependence of these contributions to the electrical resistivity on the magnesia content follows two stages: one below and another above the solubility limit of magnesia in yttria-stabilized zirconia. The same dependence is found for the lattice parameter determined by X-ray measurements. The impedance diagrams of the composites have been resolved allowing the identification of contributions due to the presence of each microstructural constituent in both stages.