Micromorphology of ZnO varistors made with seed grains shows that there are two kinds of combinations of ZnO grains. Two different micromodels of ZnO varistors are put forward according to their micromorphology. The relation between ZnO grains’ mean diameter and the amount of seed grains has been deduced from the micromodels. The relation between the electric fieldE1mA/cm2, nonlinear coefficient, and breakdown energy density of ZnO varistors and the amount of ZnO seed grains has been explained by means of micromodels. ©1995 American Institute of Physics.