Abstract: A nanocomposite material was prepared from epoxy resin reinforced by nanoceramic powder [Nano Zirconia-Yttria (Z_r O₂ -y₂ O₃) (70-80 nm)] with several weight ratios (1.5, 2.5, 3.5, 4.5 wt.%), the research samples were prepared according to the standard specifications in different thicknesses (1, 1.5, 2, 2.5 mm). The effect of addition rate (wt.%) was studied as well as the thickness, number of cycles and average of voltage increase, on the dielectric strength (E_br) for the composites before immersion, then, the effects of immersing the composite br material in distilled water as well as in NaOH and HCL diluted solutions (0.5 N) were observed. The test results revealed an increase in (E_br) with increasing the addition of Z_r O₂ -y₂ O₃) [(from 27.8 kV/mm for a ratio of 1.5 wt.% br to 33.4 kV/mm for a ratio of 4.5 wt.% at the average of voltage increase 0.5 kV/sec) (and from 31.4 kV/mm for a ratio of 1.5 wt.% to 36.7 kV/mm for a ratio of 4.5 wt.% at the average of voltage increase of 5 kV/sec)] and with increasing average voltage increase on the contrary (E_br) decreases with increasing the sample thickness, br number of cycles and immersion in distilled water and chemical solutions (with immersion period) noticing that the chemical solutions effect was greater than that of the distilled water.