Abstract: ZnO-V₂O₅-SnO₂ based varistor ceramics with 0.01-0.2mol% Bi₂O₃ were prepared.The conventional mixing-oxides procedure was adopted.The samples were sintered at 800℃ for four hours in ambient of air.The effect of Bi₂O₃ addition on the relative density,microstructure and electrical properties of the ZnVSnO ceramics were systematically investigated by means of high precision scale,SEM,XRD and an automatic I-V monitor.The results show: the relative densities of all tested samples exceed 98% of their theoretical density,indicating the increase of Bi₂O₃ within the studied range of 0.01-0.2mol% has no obvious influence upon the density of the ZnVSnO ceramics.Meanwhile,the average grain sizes of the ceramics decrease from 2.13μm to 1.54μm.As a result,the breakdown voltage of the ceramics was found to increase at the same time.Besides of ZnO main phase,all four studied samples consist of Zn₂SnO₄ and Bi₂Sn₂O₇ as their secondary phases.Samples with 0.2mol% Bi₂O₃ exhibit the optimum properties.Their breakdown field,nonlinear coefficient and leak current density of the optimum samples are 2842V/mm,51.2 and 0.0925mA/cm² respectively.