My research departed from two similar types of varistors which by electric penetrating power exposed different features of local failures (cover surface respectively core area). In order to analyse the failures origin, firstly for one varistor structure porosity, density, and grain size distribution had been measured quantitatively. Then a local mechanical characterization of strength and tensile modulus distribution in the component had been made. As further next step an electrical resistance measurement had been conducted, which was based on self-programmed routine measurement procedures, that compared varistors of type I and II in respect to distribution of resistance, varistor coefficients, and varistors voltage (at 1 mA / cm ). Based on these investigations clear conclusions could be drawn regarding the origin of local failures which were not caused by chemical composition, but by the heat treatment of these components.