The raw material for a ZnO—Pr-based varistor is mixed with cobalt and potassium to prepare a ceramic raw material powder. Potassium, which is an alkali metal, is added in the form of KClO4, KHC4H4O6, PtCl6, or K3[Co(NO2)6]. The ceramic raw material powder is pulverized by a wet process while 0.1 to 5.0 wt % of polycarboxylate dispersant is added to the powder. Such a method can produce a reliable, high-quality varistor having excellent varistor characteristics, such as varistor voltage V1mA and insulation resistance IR, and less variation in these characteristics.