The effect of spinel (MgAl2O4) addition on the ionic conductivity of 8 mol.% yttria-stabilized cubic zirconia (8YSZ) was investigated using the impedance spectroscopy. Undoped and 1, 5, 10, and 15 wt.% MgAl2O4-doped 8YSZ powders were prepared via colloidal process to ensure uniform mixing of the powders and to obtain a homogeneous microstructure. The ionic conductivity of the specimens was measured using a frequency response analyzer in the range of 100 mHz-13 MHz and 300-800 degrees C. Complex impedance analysis results of MgAl2O4-doped 8YSZ specimens showed that the grain interior resistance increased with MgAl2O4 addition; on the contrary, it also decreased the grain boundary resistance. Furthermore, while the grain interior conductivity of 8YSZ was decreased with MgAl2O4 addition, the grain boundary conductivity of 8YSZ enhanced with the presence of electronically conductive spinel oxide precipitated at the grain boundaries of 8YSZ. Moreover, the addition of MgAl2O4 to 8YSZ resulted in a decrease in grain boundary activation energies.