A varistor comprising a basic component consisting essentially of ZnO as a principal constituent and, as auxiliary components, bismuth (Bi), cobalt (Co), manganese (Mn), antimony (Sb) and nickel (Ni) in an amount, when calculated in terms of Bi.sub.2 O.sub.3, Co.sub.2 O.sub.3, MnO, Sb.sub.2 O.sub.3 and NiO, respectively, of Bi.sub.2 O.sub.3 : 0.1 to 5 mol %, Co.sub.2 O.sub.3 : 0.1 to 5 mol %, MnO: 0.1 to 5 mol %, Sb.sup.2 O.sub.3 : 0.1 to 5 mol % and NiO: 0.1 to 5 mol %; and an additional constituent comprising boron (B) in an amount, when calculated in terms of B.sub.2 O.sub.3, of 0.001 to 1 wt % based on said basic component, the Bi.sub.2 O.sub.3 of the sintered body comprising not less than 30% of .alpha.-phase . In another embodiment, the above basic component may further comprise at least one of Al, In and Ga in a prescribed amount and the above additional component may be (i) B with or without at least one of Ag and Si in a prescribed amount or (ii) a glass containing B in a prescribed amount.