Abstract: Power loss of modern stable ZnO varistor ceramics steadily decreases during the DC aging, which completely differs from the continuous increase in power loss of traditional instable ones. The anomalous aging phenomenon is beyond current understandings of classic ion migration model, and the non-Arrhenius aging characteristic makes condition assessment and life prediction unavailable. This paper reviews the aging and recovering characteristics of modern stable ZnO varistor ceramics. "Crossover" phenomena of the current-voltage characteristics in the forward direction are observed in the aged samples. Moreover, the aging is reversible because aged samples can recovery to their initial states. These aging phenomena can be well explained by the donor ion redistribution (DIR) model, which ascribes the power loss to the competition between consumption of interface states and "U"-shape distribution of donors in depletion layers. The former leads to increase in power loss while the latter leads to decreasing power loss. Stable ZnO varistor ceramics can turn into instable ones if their interface states cannot maintain stable at higher temperatures or in oxygen-deficient atmosphere. In addition, the widely employed power loss is voltage-dependent so that it is not an intrinsic condition assessment parameter for ZnO varistor ceramics. Instead, reverse aging coefficient is a potential assessment parameter. By deepening the understandings on the aging phenomena, aging mechanisms, and condition assessment, this paper aims to promote the manufacture of high-performance ZnO varistor ceramics, as well as the development of advanced arresters.