ZnO-Bi2O3-TiO2-Co2O3-MnO2-based (ZBTCM) varistors were fabricated via the conventional solid-state method, and the effect of SiO2 content on the phase transformation, microstructure, and electrical properties of the ZBTCM had been investigated. Results showed that this varistor can be sintered at a low temperature of 880 degrees C with a high sintering density above 0.95 of the ZnO theoretical density. In these components, SiO2 acts as a controller in ZnO grain growth, decreasing the grain size of ZnO from 3.67 to 1.92m, which in turn results in an increase in breakdown voltage E-1mA from 358.11 to 1080V/mm. On the other hand, SiO2 has a significant influence on the defect structure and component distribution at grain-boundary regions. When SiO2 content increases from 0 to 4wt%, the value of the interface state density (N-s) increases sharply. At the same time, the electrical properties are improved gradually, and reach an optimized value with the nonlinear coefficient () up to 54.18, the barrier height (phi(b)) up to 2.90eV, and the leakage current (I-L) down to 0.193A/cm(2).