In this present work, we studied the effect of Nickel substitution on the structural, electrical and magnetic property of NixMg1−xFe2O4 (x = 0.00, 0.10, 0.20 and 0.30) synthesized by sol–gel auto combustion technique and characterized by various method such as the X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM) and dielectric properties. The XRD pattern reveals the single phase cubic spinel structure and the lattice parameters values of range 8.368–8.394 Å were observed. Surface morphology and particle sizes were studied by using FE-SEM. The dielectric constants have been ascribed to Maxwell–Wagner and Interfacial theory in agreement with Koop’s phenomenological theory. The resistance values decrease with increasing temperature which showed negative temperature coefficient. The decreasing tendency of saturation magnetization was owing to the enhancement in the substitution of Nickel cations in Magnesium ferrites. The coercivity value increases under the control of Nickel content in Mg ferrites. The behavior of Mg–Ni ferrite is ferromagnetic at room temperature which is applied in various technological and industrial areas like magnetic sensor, high frequency device and recording tape. © 2017, Springer Science+Business Media, LLC, part of Springer Nature.