Abstract: A series of Mg1-x NixFe2O4 spinel ferrites with x = 0.0, 0.25, 0.50, 0.75 and 1.0 have been prepared using standard ceramic method. The relationship between structural parameters and concentration of the substituted Ni-ions has been studied. A determination of crystal structure, oxygen positional parameter and cation distribution using X-ray Diffraction (XRD) and R-factor method revealed that these ferrites belong to the familty of mixed of partially inverse spinels.