Co0.3Zn0.7-xNixFe2O4 (0 ≤ x ≤ 0.7) spinel ferrites were produced by the solid-state reaction method. It was shown that all samples can be characterized by the single-phase state (space group Fd-3 m). The behavior of the lattice parameters and the volume of the unit cell correlate well with the average of the ionic radii of the Zn2+ and Ni2+ and their concentration in Co0.3Zn0.7-xNixFe2O4 (0 ≤ x ≤ 0.7). The dependence of the hyperfine parameters of the Mössbauer spectra at two temperatures on the nickel content was studied. It was demonstrated that increase of the Ni content leads to the increase of the remnant magnetization and coercivity. It can be explained by the increase of the magnetic domain volume. It was concluded that electronic configuration of the Zn and Ni ions and their concentration in Co0.3Zn0.7-xNixFe2O4 (0 ≤ x ≤ 0.7) not so critically impact on magnetic properties as well as the features of the cation distribution in oxygen coordination and the peculiarities of the intra- and interlattice exchange interactions.