Ni0.8−xZnxCo0.2Fe2O4 (x = 0.0, 0.05, 0.10 and 0.20) were prepared by citrate-gel auto-combustion method. The structural investigation using powder X-ray diffraction (XRD) showed the formation of single-phase cubic spinel structures with Fd-3m space group for all prepared samples. As the Zn2+ concentration is increased, the values of the lattice constant, tetrahedral and octahedral bond lengths undergo significant change. The absolute experimental lattice parameters are closely to the Vegard’ s law derived ones, suggesting that the cations concentration fairly correspond with those calculated prior chemical synthesis. Fourier transform infrared (FTIR) absorption bands at 594–400 cm− 1 confirm the formation of spinel structure. The values of dielectric constant and loss tangent were reported to decline with frequency and the Zn2+composition (x). Incorporation of Zn at nickel-cobalt resulted in decrease in ac conductivity at RT. Here, we report a low loss tangent factor of the order of 8 × 103for the sample with x = 0.20 make this composition suitable for high frequency applications. Imaginary electric modulus studies unveil the presence of non-Debye type of dielectric relaxation phenomenon. The activation energy of our samples calculated from modulus spectra is found to increase with further substitution of Zn2+ concentration.