Ce3+-doped Mg-Co ferrite powder can be prepared by sol-gel spontaneous combustion method. The chemical formula for Mg0.2Co0.8Fe2-xCexO4 (x = 0.00, 0.025, 0.05, 0.075, 0.1). X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), and Vibrating sample magnetometer (VSM) were used for a series of structural and magnetism analysis of the samples. XRD results show that all samples were spinel structures, the lattice constants of the samples increased first and then decreased, and the sizes of all the samples were 66 similar to 88 nm. FTIR shows that the characteristic peaks and absorption bands of pure and doped samples are consistent with the characteristics of spinel, which further confirms the cubic spinel structure of the samples. SEM confirmed that the samples were spherical spinel. VSM confirmed that the saturation magnetization (Ms) and remanent magnetization (Mr) increased first and then decreased with the increase of Ce3+ content, indicating that Ce3+ content has an effect on the magnetism of ferrite. When the concentration of Ce3+ is 0.025, the values of saturation magnetization and remanent magnetization of samples are the best, and the samples have the best magnetic properties.