B2O3 doped ZnO-Bi2O3-Sb2O3-based varistors were fabricated by conventional solid state reaction method. The structure and electrical properties were investigated by XRD, SEM and electrical measurements. The grain size obviously increases with increasing B2O3 content, while the content of Zn7Sb2O12 spinel on the grain boundaries gradually decreases, which implies that B2O3 doping inhibits the growth of Zn7Sb2O12 spinel. The density (ρ) of ZnO varistors increases with increasing B2O3 content (x) and reaches the maximum at x = 0.4 mol%. The sample with x ≈ 0.6 mol% sintered at 1150 °C exhibits the best performance, with nonlinear coefficient of 48 and leakage current of 4 μA.