Impedance spectroscopy (IS) was used to measure electrical responses of various plasma-sprayed yttria-stabilized zirconia (YSZ) materials. Coupled with X-ray diffraction, scanning electron microscopy, and microindentation, the effects of heat treatment on microstructure, phase composition, and mechanical properties were investigated. Results showed electrical responses for YSZ grains and grain boundaries varied with size and position of silver electrodes used. YSZ heat treated at 950 degrees C showed micro-crack closure: at 1150 degrees C, microstructural and phase changes, and at 1450 degrees C, formation of a resistive monoclinic phase. The aim was to develop that IS as a non-destructive tool for thermal barrier coatings; results suggest IS can monitor microstructural and phase changes in YSZ under certain conditions.