Zinc oxide powder was tribophysically activated by grinding in a vibromill in a continual regime in air. Investigations based on the application of the electronic paramagnetic resonance (EPR) method were performed, with the purpose of establishing laws for defect formation from the viewpoint of the evolution of the fine defect structure of dispersed systems. The main focus was on the influence of the duration of tribophysical activation (TA) on the process of defect formation. Six signals were seen on the EPR spectra obtained. These signals were identified, which enabled definition of the evolution scheme of the defect structure in polycrystalline samples of zinc oxide during tribophysical activation by grinding, based on the established dependence of the formation of different centres from the grinding time.