Spinel ferrites have many applications in magnetic cores, ferrofluids and sensors. Obtaining improved saturation magnetization (M S ) and reasonable values of coercivity (H C ) forms the key objective in research on these ferrites. Ferrites with spinel structure, represented with general formula MFe 2 O 4 , where M is divalent metal ion such as Mn, Cu, Zn, Co, Ni. Magnetic properties of spinel ferrites depend on cation distribution in spinel structure. Many researchers have focused on the magnetic properties of nickel ferrites doped with metal ions that provide improved magnetic properties for industrial and medical applications. In this thesis, Cr and Zn-substituted nickel ferrites, general formula Ni 1-x Zn x Fe 2-x Cr x O 4 (x = 0, 0.1, 0.3, 0.5, 0.7), were prepared using the sol- gel auto- combustion method. For precise analysis, the Ni 1-x Zn x Fe 2 O 4 and NiFe 2-x Cr x O 4 (x = 0, 0.1, 0.3, 0.5, 0.7) samples were also checked individually. The effects of Cr and Zn doping on the structural, morphological, and magnetic properties of the samples were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The full pattern fitting of Rietveld method using MAUD program confirmed the crystalline structure and phase purity of all the ferrites. SEM images showed that the particles were in the nanosize range. VSM results revealed that the values of M S in the NiFe 2-x Cr x O 4 samples decreased and H C had no regular behavior with increasing Cr content. The maximum value of H C = 165 Oe was obtained for a Cr content of x = 0.7. On the other hand, saturation magnetization values initially increased in both the Ni 1-x Zn x Fe 2-x Cr x O 4 and Ni 1-x Zn x Fe 2 O 4 samples, with changing the doping level up to x = 0.3, while for further content, M S decreased. In addition, H C decreased with increasing doping level. In the other part of thesis, the effects of sintering temperatures on structural and magnetic properties of Ni 1-x Zn x Fe 2-x Cr x O 4 samples were studied. Samples were thermally treated at two temperatures of 600 and 1000 °C. Rietveld method from fitting XRD data was employed to obtain cation distribution of samples. The integrated intensity ratios I 220 / I 222 and I 220 / I 422 analysis indicated changes in the cation occupancy with sintering temperature. As expected, the mean particle size increased with sintering temperatures. VSM results showed that saturation magnetization increased with increasing of sintering temperature. The increments of saturation magnetization with sintering temperature could be related to particle size and cation redistribution. Also saturation magnetization reduced with increasing of Zn-Cr doping level x at 600 0 C sintering temperature. It is related to cation redistribution. Generally, with increasing sintering temperature, H C decreased. But it is observed that H C values decreased for the doping level of x ? 0.3, while for further content, Hc increased with increasing sintering temperature.