Yttria-zirconia electrolytes of 3 and 8 mol% Y2O3 nominal content have been prepared by sintering in a microwave furnace under several different conditions to obtain crack-free high density specimens. The ionic conductivity of both compositions has been investigated with a four-probe DC technique as a function of temperature over the 400 degrees-1000 degrees C range and as a function of time at the normal fuel cell operating temperature of 1000 degrees C. Impedance spectroscopy has been used to separate the grain boundary contribution to the total resistivity. The results have been compared with conventionally sintered (radiant heat) materials.