Mg-doped ZnFe2O4 samples were prepared by a microwave combustion method. The obtained samples were characterized by powder X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis, UV–Visible diffuse reflectance spectra (DRS), photoluminescence (PL) spectra and vibrating sample magnetometer (VSM). XRD results confirm the formation of cubic spinel-type structure with an average crystallite size in the range of 15–43nm. Lattice parameter decreases with increasing Mg concentration, due to the smaller ionic radius of Mg2+ ion. The HR-SEM images show the morphology of the samples as spherical shaped particles in agglomeration. The broad visible emission band is observed in the entire PL spectrum. The estimated band gap energy is found to decrease with increasing Mg content (2.15–1.42eV). The magnetization showed an increasing trend with increasing Mg concentration (x=0.5), due to the rearrangement of cations at tetrahedral and octahedral sites