In the present study the epoxy nanocomposites are water aged- dried and the cyclic process was repeated for two cycles. The % of water uptake at the point of saturation has maximum values of approximately 2.5 and 1.5 % for first and second round of aging respectively, followed by water diffusion coefficient were calculated for 0, 1, 3 and 5 wt% MgO filled epoxy nanocomposites. The results indicates that the % of water uptake was decreased for all the samples during second cycle. 3wt% MgO filled nanocomposite showed optimum % of water uptake. The dielectric properties of unaged and water aged MgO filled epoxy nanocomposites were studied using dielectric spectroscopy and compared with the neat epoxy. The real permittivity (e') of the nanocomposites showed increased permittivity on water diffusion to the bulk material. The space charge behavior of unaged and water aged specimens were carried out by using PEA studies. Water aged samples has showed faster space charge decay. Also, the accumulated space charge density was high with water aged specimens. Also the local electric field variation is reduced in the second cycle of water ageing. © 2020 Institute of Electrical Engineers of Japan. All rights reserved.