Electrical treeing in LDPE and three LDPE nanocomposites, with spherical silica and fibrous and laminar phyllosilicates, has been studied. Electrical tests were performed at a 50 Hz frequency and voltages between 8 and 29 kV, and the time to inception of the first electrical partial discharges (TTI) of the electrical trees and the time to breakdown (TBD), related to the electrical stability of the insulator, were determined. Above 15 kV all the nanocomposites show longer inception times and shorter tree growth times than LDPE. It is proposed that both observations are caused by the modification of the polymer crystalline morphology induced by the presence of the fillers and by the development of a large number of interfacial structures, both organo–inorganic and amorphous–crystalline. Below 15 kV the TBD is increased in the nanocomposites with the laminar silicate because of tortuosity and the TTI is increased in the fibrous silicate containing a nanocomposite because of the LDPE crystalline morphology in the presence of the silicate. The nanosilica particles decrease the electrical stability in the whole voltage range by decreasing both TTI and TBD.