We prepared Ni nanoferrite (NiFe2O4) via sol–gel-process, study thermal annealing (~400 − 600 °C/2 h) dependent structural, dielectric properties, probed by X-ray diffraction (XRD), dielectric-response. XRD shows spinel phase (grain size: 25.43 nm − 76.26 nm), Fe2O3 phase. Increase of annealing temperature shows: decrease of lattice parameter; on B-site: Fe3+-ions increases, Ni2+-ions decreases; observed strain range between 3.0 × 10−3 −  3.8 × 10−3 ascribable to the modification of cationic distribution. Dielectric properties also display noticeable changes with annealing temperature. Dielectric constant \(\epsilon^{\prime},\,\epsilon^{\prime\prime}\) decays at higher frequency while at lower frequencies it increases. Conductivity (σac) remains constant at lower-frequency, whereas at higher frequencies it increases sharply. Although, conduction process is explained by motion of charges, grain boundaries, space charge distribution, results also reveal that polarizability strength varies weakly with annealing temperature, correlated barrier hopping remains the dominant mechanism for conduction. Complex permittivity ( \(\epsilon^{\prime},\,\epsilon^{\prime\prime}\) ), and corresponding impedance ( \(z^{\prime},\, z^{\prime\prime}\) ) data represented using the Cole—Cole plots are ascribable to the increasing grain-boundary effects. With increasing frequency, decrease of loss tangent, improvement of conductivity (σac) makes the studied samples promising materials for high frequency device applications.