Nanocrystalline ferrites are known to be used in different type of applications involving electronic, electrical, wastewater management industry and more recently, as sensible materials. The changes occurred in their electric and magnetic properties when are stressed by an external stimulus can or cannot recommend them as sensitive materials. Before testing the sensibility for a specific stimulus, detailed analyzes of materials must be carried out. Four samples with nominal composition NiFe2O4, NiFe1.90Ce0.10O4, Ni0.4Cu0.6Fe2O4 and Ni0.4Cu0.6Fe1.90Ce0.10O4 were obtained by coprecipitation technique [1]. All samples were calcinated at 600°C for 6h in order to form the specific cubic type spinel phase with Fd-3m space group. The newly obtained ferrite powders were pressed into pellets using a 13 mm matrix and sintered at 950°C for 6h. Visible differences such as color and diameter changes were noticed between the samples, indicating porosity or structural modifications, like those occurred in copper cerium doped ferrites (CuFe2-xCexO4) thermal treated at 600°C and 950°C [2]. X-ray analysis and Rietveld refinement technique were used to identify and calculate the quantity of phases present in samples. The results suggested the formation of cubic spinel ferrite as the main phase. For several samples, small quantities of secondary phases such as a-Fe2O3, CuO and CeO2 were identified. Magnetic values such as remanent magnetization (Mr), saturation magnetization (Ms) and coercivity (Hc) were determined by VSM (vibrating sample magnetometry) technique in an applied magnetic field of ±10 kOe. The M-H loops of all samples showed an ferrimagnetic behavior, typical for a soft magnetic material, even if the magnetic values raised after the 950°C thermal treatment. The XRD results indicated a structural instability for cerium doped ferrites due to CeO2 presence in both calcinated and sintered samples. For the NiFe1.90Ce0.10O4 sample, the CeO2 content rises from 1.30 wt% to 3.30 wt% after the 950°C treatment and for Ni0.4Cu0.6Fe1.90Ce0.10O4 sample from 0.50 wt% to 2.90 wt%. This raise of CeO2 phase demonstrate the mobility of Ce3+ cations which are unable remain in a higher crystallinity degree spinel structure.