The main aim of the present study is to evaluate the impact of the nano-ZnO on the dielectric properties of alumina bodies used in high voltage insulators. In this work, Zinc oxide/alumina nanocomposites were prepared by sol–gel method. The ratios of ZnO were 5, 6 and 7 mass %. The effect of ZnO on the densification, microstructure, mechanical and electrical properties of the prepared bodies were evaluated after sintering at a temperature ranging from 1550 to 1750 °C. Results revealed that incorporation of 7 mass % ZnO enhanced the breakdown voltage, electric resistivity and the dielectric loss, which are the most important factors to evaluate high-voltage insulators. In addition, incorporation of 7 mass % ZnO enhanced the densification and mechanical properties of the alumina nano composites .