Nanocrystalline zinc substituted nickel ferrites, Ni_1-xZn_xFe₂O₄ (0.0≤x≤1.0) have been prepared by citrate gel auto-combustion method. The effect of zinc ion content on structural, electrical transport and magnetic properties has been studied. The X-ray diffraction (XRD) pattern revealed that, all the compositions possess single-phase spinel structure. The nano-sized grain structure formation was confirmed by transmission electron microscopy (TEM). The dc electrical resistivity shows the samples are semiconducting in nature. The magnetic measurements showed that the composition Ni_0.6Zn_0.4Fe₂O₄ has maximum saturation magnetization (Ms) while high coersivity (Hc) for ZnFe₂O₄. Thermoelectric power measurement study showed that the compounds, with x≤0.4 are p-type and for x > 0.4 behaves n-type conduction mechanism.