The electrical stability for DC stress of Pr$_{6}$O$_{11}$-based ZnO varistos consisting of ZnO-Pr$_{6}$O$_{11}$-CoO-Cr$_2$O$_3$-Er$_2$O$_3$-based ceramics were investigated with sintering temperature in the range of 1325~1345$^{circ}C$. A the sintering temperature is raised, the nonlinear exponent of varistors was decreased, whereas the stability was markedly improved. The density of ceramics was found to greatly affect the electrical stability for DC stress. The varistors sintered at 13$25^{circ}C$ were completely degraded because of thermal runaway attributing to low density. The varistors sintered at 1335$^{circ}C$ exhibited the highest nonlinearity, with a nonlinear exponent of 70.53 and a leakage current of 1.92$mu$A, whereas they did not exhibit relatively high stability. On the contrary, the varistors sintered at >134$0^{circ}C$ exhibited not only a high nonlinearity marking the nonlinear exponent above 50 and the leakage current below 3$mu$A, but also a high stability marking the variation rate of the varistor voltage below 2%, even under DC stress such as (0.80V$_{1mA}$/9$0^{circ}C$/12h)+(0.85V$_{1mA}$/115$^{circ}C$/12h)+(0.90V$_{1mA}$/12$0^{circ}C$/12h)+(0.95V$_{1mA}$/1$25^{circ}C$/12h)+(0.95V$_{1mA}$/15$0^{circ}C$/12h). In particular, ti was found that the varistors sintered at 134$0^{circ}C$ were more nonlinear and more stable, compared with that of 1345$^{circ}C$.EX>.}C$</TEX>.EX>.