The conduction mechanism in ZnO varistors has been studied assuming thermionic emission as the only way of charge transport. A model elaborated on that basis has been satisfactorily applied to the approximation of theI–UandC–Ucharacteristics and has made it possible to determine the barrier height &Fgr;b(300 K)=0.86 V, the donor concentrationND&bartil;1019cm−3, the effective number of grains between the electrodesg&bartil;20, the position of the Fermi levelEC−EF&bartil;0.07 eV, and the donor levelEC−ED&bartil;0.20 eV. The relative power spectral density of 1/fcurrent fluctuationsSI/I2in the varistors in the ohmic region has been calculated, starting from the mobility fluctuation approach of the 1/fnoise. The calculated linear relationship betweenSI/I2and the varistor resistance in the ohmic region has been confirmed by the experimental results. The calculated 1/fnoise density is in agreement with the observed density.