The present invention relates to a zinc oxide varistor as a characteristic element of an arrestor for protecting a transmission and distribution line and peripheral devices thereof from surge voltage created by lightning, and more particularly a highly reliable zinc oxide varistor excellent in the non-linearity with respect to voltage, the discharge withstand current rating properties, and the life characteristics under voltage, a method of preparing the same, and PbO type crystallized glass for coating oxide ceramics employed for a zinc oxide varistor, etc. A zinc oxide varistor of the present invention comprises a sintered body (1) and a high resistive side layer (3) consisting of crystallized glass with high crystallinity containing the prescribed amount of SiO.sub.2, MoO.sub.3, WO.sub.3, TiO.sub.2, NiO, etc., formed on the sides of the sintered body (1) to enhance the strength and the insulating property thereof, thereby improving the non-linearity with respect to voltage, the discharge withstand current rating properties and the life characteristics under voltage. The crystallized glass composition for coating of the present invention comprises PbO as a main component and additives such as ZnO, B.sub.2 O.sub.3 , SiO.sub.2, MoO.sub.3, WO.sub.3, TiO.sub.2, and NiO to enhance the crystallinity and the insulating property thereof.