The microstructure, electrical and dielectric characteristics of $ZnO-{Pr}_6{O}_11-{CoO}-{Dy}_2{O}_3$-based varistors were investigated without and with various metal oxide additives(NiO, MgO, Cr$_2$O$_3$). The average grain size decreased in the range of 18.4 $acksim$ 11.5 $mu$m, in order of NiOlongrightarrowMgOlongrightarrow{Cr}_2{O}_3$ and the density decreased in the range of 5.62 acksim 5.33 $g/{cm}^3$ in order of NiOlongrightarrowCr$_2$O$_3$longrightarrowMgO. While, the nonlinear exponent increased In the range of 19.8</TEX>$acksim$</TEX>67.4 in order of NiOlongrightarrowMgOlongrightarrow${Cr}_2{O}_3$ and the leakage current decreased in the range of 25.6 $acksim$ 1.2 $mu$A in order of NiOlongrightarrow${Cr}_2{O}_3$longrightarrowMgO. Among all varistors, the Cr$_2$O$_3$-added varistor exhibited the highest nonlinearity, with a nonlinear exponent of 67.4 and a leakage current of 1.2 $mu$A. Furthermore, this varistor exhibited the lowest dielectric dissipation factor of 0.0407.