PD (partial discharge) resistance is prominent in polymer nanocomposites, which is enhanced by nano- segmentation of matrices, tight coupling in interfaces, and pile-up of nano fillers on surfaces. Treeing resistance is determined by partial dielectric breakdown of solids to produce initial trees followed by widening and extending hollow channels due to internal PDs. Therefore, treeing turns out to be related to PD resistance, when PDs are predominant in treeing breakdown. Such phenomena were actually observed in epoxy nanocomposites. Similar aging processes are considered to be underlying in both treeing lifetime and PD resistance. Such similarity is discussed and substantiated by SEM images of tree channels.