When sintered 2Y-TZP (2 m/o yttria doped tetragonal zirconia polycrystals) specimens were embedded in ZrN powder and heat-treated at 1700 degreesC, the cubic phase was stabilized as a result of nitrogen incorporation. The resultant microstructure was similar to a columnar zone in a metal alloy ingot. elongated grains were developed with their length parallel to the nitrogen flux into the specimen. Impedance measurements were made on the nitrogen-stabilized zirconia along the length direction of the columnar grains and perpendicular to the length direction, respectively. The: boundary effects of the columnar grains were thus unequivocally distinguished. Different activation energies for the grain boundary and bulk conductivity support the blocking nature of the boundaries in nitrogen-stabilized zirconia as well as in 2Y-TZP. SEM and TEM analyses revealed that the nitrogen-stabilized zirconia consists of a matrix of a cubic phase containing a dispersion of tetragonal precipitates similar to the PSZ (partially stabilized zirconia). No continuous glassy phase at the grain boundaries was identified in the nitrogen-stabilized zirconia as well as in the 2Y-TZP ceramics. The grain boundary resistance was ascribed to a depletion space charge layer at the grain boundary.