Because of their unusual properties – non-ohmic behavior and the ability to absorb a lot of energy – metal-oxide varistors are widely used for the protection of electrical and electronic devices against over-voltages. ZnO ceramics have varistor properties because of their metal-oxide additives and the microstructures developed during sintering. The value of the varistor voltage depends largely on the number of conducting ZnO grains between the electrodes; this can be set by controlling the thickness of the device or the size of the grains. The desired grain size can be achieved by altering the composition of the metal-oxide additives and the sintering conditions. In this work the grain growth was controlled by combining two ZnO powders of differing sinterability in the starting material. Also, the use of BaBiO2.77 as a precursor for Bi2O3 is an innovation in varistor technology that makes it possible to reduce the amount of added metal oxides. As a result, a variety of varistors with good varistor properties and a wide range of working parameters were produced.