The microstructure and electrical properties of $ZnO-Pr_{6}$$O_{11}$ $-CoO-Y_2$$O_3$-based varistors were investigated with and without various metal oxide additives (NiO, MgO, and $Cr_2$$O_3$). The addition of NiO promoted the grain growth while that of Cr$_2$O$_3$ decreased average grain size. Thereby, the varistor voltage was higher in $Cr_2$$O_3$-added composition. Among $ZnO-Pr_{6}$ $O_{11}$ /$-CoO-Y_2$$O_3$-based varistors, the$ Cr_2$$O_3$-added varistor exhibited the highest nonlinear exponent (51.2), the lowest leakage current (1.3 $mu$A), and the lowest dielectric dissipation factor (0.0433).