Nano-crystalline Zn1-xNixFe2O4 (x = 0.0 - 1.0) nano-ferrites were synthesized by using sol-gel auto-combustion method. X-ray diffraction (XRD), magnetic measurements were used to monitor the effect of Ni addition on structural, magnetic properties. XRD patterns confirm the formation of single phase nanocrystalline cubic spinel structure. For sample with x = 1.0, a small fraction of Fe2O3 was also detected. Calculated parameters revealed that Ni2+ addition changecrystallite sizes (D-s) and (DW-H) respectively in the range between 30.29 - 39.13 nm, and 37.52 - 64.57 nm. Observed changes in the cell volume (V), specific surface area (S), X-ray density (rho(XRD)), are attributed to the difference in ionic radii of Fe3+, Ni2+, Zn2+ ions. The Ni2+ ions migrate predominantly to octahedral sites (thus pushing ferric ions on A sites) leading to increased inversion parameter and decrease of oxygen parameter (u) from 0.3836 to 0.3796. Exact matching of a(exp), a(th) suggests that the estimated cation distribution is in good agreement with the real distribution and with magnetic data obtained from VSM. H-c varies between 66.49 Oe- 185.20 Oe, while, migration of cations leads to changes in M-s. In order to explain the nature of the surface defects the antistructural model is used in the current study.