This communication reports on the preparation and electric properties of dense nanocrystalline ZnO ceramics. By spark plasma sintering, nanocrystalline (similar to100 nm) ZnO ceramics with a high density of 98.5% were obtained at a very low temperature of 550degreesC. Electric property measurement revealed a novel conduction nonlinearity in the sample sintered at 500degreesC. This phenomenon is due to the nanometerization of ZnO crystal and the grain boundary layer with an amorphous interfacial layer.