Magnesium ferrite nano-crystallites are synthesized by hydrothermal technique. The pure cubic spinnel phases are formed there by microwave heating at 500°C for 10 min. Average crystallite size is found to be of order 42.4 nm using diffraction studies. The largest specific surface area of 65.1 m2/g is achieved for MgFe2O4 nano-crystallites. The morphology is analysed by field emission scanning electron microscope and transmission electron microscope. Dielectric studies reports the dielectric constant (ϵr) of 12.6 and low loss tangent (tan δe) 0.067 which are suitable for microwave device applications. Low ac-conductivity (σac) of 2.4 x10-6 S/cm is obtained for nano ferrite. © 2016 Elsevier Ltd. All rights reserved.