The microstructure and electrical properties of Er2O3-doped ZnO-V2O5-MnO2-Nb2O5 varistor ceramics were investigated with different contents of Er2O3. Increasing content of Er2O3 increased the sintered density (5.51-5.61 g/cm(3) for Er2O3-doped samples) and reduced the average grain size (5.2-5.7 mu m). With increasing content of Er2O3, the breakdown field increased from 4800 to 5444 V/cm up to 0.05 mol%, whereas a further increase decreased it. The maximum nonlinear coefficient was 63, which was from the addition of 0.05 mol% Er2O3. The donor concentration increased from 4.21 x 10(17) to 1.04 x 10(18) cm(-3) with increasing content of Er2O3 and the barrier height exhibited a maximum value (1.21 eV) at 0.05 mol% Er2O3.