Bulk and nano Ni1-xMgxFe2O4 (x = 0-1) samples were synthesized via microwave double sintering and microwave assisted hydrothermal techniques respectively. The diffraction pattern confirmed the formation of cubic spinel phases in case of both the ferrites. The larger bulk densities were achieved to the bulk than that of nano. In addition, a comparative study on X-band (8.4-12 GHz) electromagnetic interference shielding properties of current bulk and nanomaterials was elucidated. The results showed that the bulk Ni0.6Mg0.4Fe2O4 composition revealed the highest total shielding efficiency (SET) of similar to 17 dB. In comparison, the shielding efficiency values of all bulk contents were higher than that of nano because of larger bulk densities. Moreover, the ac-electromagnetic parameters such as electrical conductivity (sigma(ac)), the respective real (epsilon' & mu') and imaginary parts (epsilon '' & mu '') of complex permittivity and permeability were investigated as a function of gigahertz frequency. The bulk ferrites of x = 0.4 & 0.6 showed the high epsilon '' of 10.26 & 6.71 and mu '' of 3.65 & 3.09 respectively at 12 GHz which can work as promising microwave absorber materials. Interestingly, nanoferrites exhibited negative mu '' values at few frequencies due to geometrical effects which improves the microwave absorption. (C) 2016 Elsevier B.V. All rights reserved.