• The cobalt ferrite nanoparticles doped with ytterbium elements are synthesized by means of the hydrothermal method . • Micrographs obtained by FESEM showed spherical shapes for nanoparticles with and average particles size is found to be 30–45 nm. • We found a ∼90% increase in H C by 10% Yb doping. • Yb doping does not significantly affect the saturation magnetization of the cobalt ferrite nanoparticles. The low coercivity of spinel ferrites is a significant barrier limiting their use in high-density magnetic recording applications. The large magnitude of the magnetocrystalline anisotropy of the rare earth group elements can lead to a high coercivity field by doping the magnetic ferrites with these elements. In this research, using the hydrothermal method, Fe +3 in cobalt ferrite was substituted with Yb +3 to make CoFe 2-x Yb x O 4 with x = 0, 0.025, 0.05, 0.075, and 0.1. By analyzing the X-ray diffraction analysis and confirming the spinel structure, the crystallite sizes were obtained in the range of 31 nm to 45 nm. The lattice parameter was estimated to be in the range of 8.30 nm to 8.36 nm. The FTIR analysis of the nanoparticles showed the ν 1 absorption band in the range 584 Cm −1 to 594 Cm −1 . The Raman spectroscopy analysis showed that CoFe 2-x Yb x O 4 nanoparticles have a mixed spinel structure. Hysteresis loops at room temperature and 10 K obtained by the vibrating sample magnetometer (VSM) indicate that the coercivity field (H C ) increases significantly from 0.55 to 1.05 KOe and 9.48 to 12.00 KOe, respectively, by increasing Yb doping from x = 0 to x = 0.1.