The electrical properties and stability of $ZnO-Pr_6O_{11}-CoO-Cr_2O_3-based$ varistors were investigated for different $Tb_4O_{11}$ amounts in the range of $0{sim}1.0;mol%$. As the $Tb_4O_{11}$ amount increased, the sintered density increased in the range of $99.1{sim}101.1%$ of theoretical density and the average grain size decreased in the range of $7.7{sim}4.8{mu}m$. The varistor voltage increased in the range of $280.9{sim}715.8V/mm$ and the nonlinear coefficient increased in the range of $26.4{sim}44.4$ with the increased of $Tb_4O_{11}$ amount. The 0.25 mol% $Tb_4O_{11}$-doped varistors exhibited the high electrical stability, with -0.1% in variation rate of varistor voltage, -0.7% in variation rate of nonlinear coefficient, and +17.4% in variation rate of leakage current for specified dc accelerated aging stress of $0.95V_{1mA}/150^{circ}C/24h$.