Structural, surface morphological and magnetic properties of polycrystalline Ni0.50Zn0.50-x-yMgxCryFe2O4 (for x=0.0, 0.1, 0.2 and y=0.0, 0.1, 0.1) were thoroughly investigated. The lattice parameters of the samples investigated are found to decrease with increasing Mg and Cr contents. The bulk density and the average grain diameter are found to decrease with increasing Mg and Cr substitution in Ni0.50Zn0.50-x-yMgxCryFe2O4 for any particular sintering temperature. However, they are found to increase with increasing sintering temperatures for any individual composition. In the present investigation, the maximum bulk density and the largest average grain diameter are found for Ni0.50Zn0.50Fe2O4 sintered at 1350 degrees C. The observed variation of lattice parameters and bulk densities of the samples investigated are explained with the help of ionic radii and atomic masses of the substituted cations. The real part of initial permeability, mu(i)', and the saturation magnetization, M-s, are found to decrease with increasing Mg and Cr contents in Ni0.50Zn0.50-x-yMgxCryFe2O4, whereas the Neel temperature, T-N, increases. The highest mu(i)', the value of which is 432, is obtained for Ni0.50Zn0.50Fe2O4 (x = 0, y = 0) composition sintered at 1350 degrees C with corresponding resonance frequency, f(r) of 2 MHz. On the other hand, the highest f(r) (45 MHz) is obtained for Ni0.50Zn0.2Mg0.2Cr0.1Fe2O4 Sintered at 1250 degrees C with corresponding mu(i)' = 88. The relative quality factor, Q, decreases with increasing Mg and Cr contents. The highest Q values for Ni0.50Zn0.50Fe2O4 and Ni0.50Zn0.3Mg0.1Cr0.1Fe2O4 are observed for the samples sintered at 1250 degrees C. On the other hand, the highest Q value for Ni0.50Zn0.2Mg0.2Cr0.1Fe2O4 is obtained for the sample sintered at 1350 degrees C. The observed mu(i)' values and M, are related to the chemical composition, morphological nature of the grain boundaries and average grain diameters. It is also observed that increase of mu(i)' is accompanied by the decrease of f(r), which confirms the Snoek relation for polycrystalline ferrites. (C) 2008 Elsevier B.V. All rights reserved.