Ferromagnetic and ferroelectric characteristics of Gd and Nd-substituted nickel ferrite were investigated. The materials formed in the cubic inverse spinel phase with small amounts of GdFeO3 and NdFeO3 as the additional phases in the respective materials. Substitution of Gd and Nd for Fe caused decrease in the saturation magnetization and Curie temperature of the nickel ferrite. However, the saturation magnetostriction is seen not to change significantly by the substitution of Gd and Nd. The existence of the ferroelectricity was confirmed from the ferroelectric loops and magnetocapacitance of -2% and -3% were observed. The large frequency dependence of the (high) dielectric constant reveals a wide dispersion of relaxation times. The ferroelectric transition temperature values of NiO.Fe1.95Gd0.05O3 and NiO.Fe1.95Nd0.05O3 were found to be 498 and 544 K, respectively. © 2009 Elsevier B.V. All rights reserved.