In this paper we present the structural, magnetic and dielectric properties of ceramic nickel manganite NiMn 2 O 4+δ produced by using nickel permanganate Ni(MnO 4) 2 xH 2 O as a precursor. We have characterized the NiMn 2 O 4+δ stoichiometry using quantitative energy-dispersive analysis of X-rays and thermal gravimetry under reducing conditions. Increased oxygen and Mn 4+ contents were detected. X-ray diffraction and Rietveld refinement of X-ray data were carried out. Temperature dependent magnetization measurements were performed and the ferri-magnetic transition was identified at ≈100 K. The ferri-magnetic moment was found to be ≈1μ B and hysteretic magnetization vs applied field curves were obtained. Dielectric properties were measured using impedance spectroscopy. Two dielectric relaxation processes were detected, which were associated with grain boundary and bulk contributions. The Arrhenius plots of resistivity and the temperature dependent dielectric permittivity were obtained for the two relaxations by means of an equivalent circuit model based on a series of two parallel RC elements.