Microstructure and electrical properties of ZnO varistors as a function of sintering temperature and times were investigated. Sintering temperature and times greatly affected electrical properties and Bi-rich liquid phase of the microstructure. The varistor which were sintered at $1125^{circ}Csim1150^{circ}C$, for 2 hr exhibited the varistor voltage$(V_c)$, nonlinear coefficient $(V_{10mA}/V_{1mA})$, leakage current$(I_L)$ dielectric constant and dissipation factor as $225sim250V/mm,;0.89sim0.92,;0.8sim1.1{mu}A,;720sim740;and;1.8sim2.0%$, respectively.