The grain-boundary conductivity of a 15 mol % calcia-stabilized zirconia specimen was increased about seven times by postsintering heat-treatment at 1300 degreesC for 10 h. From the change in the crystallinity, morphology, and composition of the intergranular phase by heat-treatment, the de-wetting behavior of the intergranular phase due to crystallization was suggested to decrease the current constriction near the grain boundary. The postsintering heat-treatment was also effective at the high sintering temperature where adding Al2O3 could not scavenge the resistive intergranular phase. (C) 2003 The Electrochemical Society.