The effect of heating rate on the microstructure and electrical properties of ZnO-Bi2O3-Sb2O3-Co2O3-MnO2-Cr2O3-SiO2 varistors was investigated. ZnO grains grow rapidly with decreasing the heating rate from 3 ℃/min to 1.5 ℃/min, resulting in the deterioration of the uniformity of the sample structure. When the heating rate increases from 3 ℃/min to 10 ℃/min, the defect diffusion becomes weakly, hindering the formation of the double Schottky barrier. When the heating rate is 3 ℃/min, the maximum nonlinear coefficient of the sample is 43.4, the minimum leakage current is 1.0 μA/cm2, the voltage gradient is 448 V/mm, the standard deviation is the minimum, and the stability of the sample is the optimum. The loss tangent tanδ under the action of an electric field at 200 Hz-2 MHz is less than 0.03. The optimum overall electrical performance of ZnO varistor can be obtained at a heating rate of 3 ℃/min. Also, the existence of the negatively charged a Bi-rich phase (i.e., Bi3.73Sb0.27O6.0+x) at the grain boundary has an influence on the electrical properties of ZnO varistors.