Effect of Mg doping on structural and magnetic properties of nano cobalt ferrites prepared via sol-gel auto-combustion method is reported. The sintered samples (Co1-xMgxFe2O4, where x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were characterized using X-ray diffraction, Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer. Rietveld refinement of X-ray diffraction spectra shows the single phase cubic structure (space group Fd3m) for the prepared samples. Raman spectroscopy reveals a doublet-like peak behavior in A(1g) and E-g modes arising due to different ionic radii of Co/Mg and Fe ions. Two prominent vibration frequencies in FTIR spectroscopy data also confirm the cubic spinel structure in the prepared samples. The magnetic parameters such as saturation magnetization, coercivity and remanence are studied with increasing the Mg-concentration in cobalt ferrite. Systematic changes in magnetic properties while going from x=0 to 1 are discussed. (C) 2016 Elsevier Ltd. All rights reserved.