Impedance spectroscopy and microstructural/analytical characterization by scanning electron microscopy/energy dispersive spectroscopy were used to study ceramic-glass composites consisting of a soda-lime glass (up to 20 weight percent) and yttria-stabilized zirconia (YSZ) fired at different temperatures (1300 to 1600 degrees C) and for different lengths of time (2 to 4 h). At low temperature, with increasing glass content, the high frequency impedance are increases slightly in a predictable manner due to the dielectric characteristics of glass and YSZ. However, the glass content causes enormous changes in the magnitude of the intermediate frequency impedance are, reaching values exceeding by orders of magnitude the values usually observed for grain boundaries in the pure electrolyte. Also, a significant shift in the relaxation frequency of this are to lower frequencies was noted with increasing glass content. This relaxation frequency is determined by the YSZ glass interface response, and this information can be used to monitor the electrolyte corrosion condition, for example in oxygen sensors operating in glass melting furnaces. Formation of Y3+-depleted electrolyte grains because of diffusion of Y3+ to the glass phase confirmed that the mechanical failure of the electrolyte was due to formation of monoclinic zirconia.