Cobalt ferrite (CoFe2O4) is a highly anisotropic magnetic material due to the magnetocrystalline anisotropy contribution from Co2+. The addition of foreign cations of different oxidation states, substituting Co2+ or Fe3+, can lead to an atomic rearrangement in the tetrahedral and octahedral sites of the ferrite structure and, consequently, modify its magnetic properties. On that basis, bare and rare earth ions (Yb3+ and Gd3+)-doped cobalt ferrite nanocrystals have been synthesized by a modified coprecipitation method. Produced nanocrystals were characterized by X-Ray Diffraction, Vibrating Sample Magnetometry and Mössbauer Spectroscopy. Small amounts of dopant species (atomic fractions of 0.01 for Gd3+ or 0.007 for Yb3+) caused an increase in room-temperature coercivity from 3.8 kOe (pure ferrite) up to 5.0 kOe. The attained coercivity is very close to the maximum value (5.3 kOe) predicted for this material. Mössbauer Spectroscopy suggested the presence of superparamagnetic particles in the powders. Also, the cation distribution did not show any noticeable change in both doped systems.