The structural and magnetic properties of Mg substituted Ni0.50Zn0.50-xMgxFe2O4 (where x = 0.0, 0.10, 0.20, 0.30, 0.40 and 0.50) sintered at various temperatures have been studied thoroughly. X-ray diffraction patterns of the samples showed single-phase cubic spinel structure without any detectable impurity phases. The lattice parameter decreases linearly with increase of Mg contents obeying Vegard's law. The bulk density, average grain size and initial permeability, mu(i)', decrease with increasing Mg substitution but increase with increasing sintering temperature for a particular composition. The highest initial permeability and quality factor, Q are obtained for the Ni0.50Zn0.50Fe2O4 sintered at 1350 and 1250 C, respectively. Domain wall relaxation frequency, f(r), and Neel temperature, T-N, are found to increase with Mg substitution. It is observed that when Zn is completely substituted by Mg in Ni0.50Zn0.50-xMgxFe2O4, the Try is increased by 106% and fr by 178%. On the other hand, mu(i)' decreases by 86%. It is observed that all samples are in ferrimagnetic state at room temperature. The number of Bohr magneton, n(mu(B)), decreases with increasing Mg substitution which is explained by probable cation distribution in the spinel crystal structure. Possible explanation for the observed features of microstructure, initial permeability, DC magnetization and Neel temperature of the studied samples are discussed. (C) 2009 Elsevier B.V. All rights reserved.