Nanocrystalline Al3+ ions doped Mg0.2Mn0.5Ni0.3AlyFe2-yO4 compositions, where y=0.0, 0.05 and 0.10 have been synthesized by citrate precursor method. The X-ray diffraction (XRD) revealed that the ferrite has single phase cubic spinel structure. The calculated particle size from XRD data have been verified using transmission electron microscopy (TEM). TEM photographs show that the ferrite powders consist of nanometer-sized particle. It was observed that the particle size decreases as the non-magnetic Al content increases. A decrease in lattice parameter and saturation magnetization with increase in aluminium concentration was attributed to smaller ionic radius and weakening of exchange interaction. Dependence of Mössbauer parameters such as isomer shift, quadrupole splitting and hyperfine magnetic field on Al 3+ ions concentration have been discussed. Initial permeability ‘µi’, relative loss factor (RLF), saturation magnetization and remanent magnetization decreases with increasing substitution of Al 3+ ions. The dielectric constant and dielectric loss decreases with increase in non magnetic Al 3+ ions. The dielectric constant follows the Maxwell–Wagner interfacial polarization. The electrical conduction in these ferrites is explained on the basis of the hopping mechanism.