It has been well established that a fine tuning in cobalt ferrite nanocrystal size within the single domain region would lead to the achievement of extremely high coercivity values at room-temperature. If so, the high coercivity and chemical stability expected for this ferrite will increase its attractiveness for magneto-optical recording applications. The present work addresses the development of a size-sensitive phase separation method for cobalt ferrite nanocrystals that is based on selective dissolution of the superparamagnetic fraction and subsequent size-sensitive magnetic separation of single domain nanoparticles. Ferrite nanocrystals synthesized under size-controlled conditions were first contacted with acidic solutions under precise conditions of acid concentration and contact time, followed by a magnetically assisted phase separation in water. Produced nanocrystals were characterized by x-ray diffraction, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), vibrating sample magnetometry (VSM), and Mössbauer spectroscopy techniques. The attained coercivity value of 9.4 kOe was mainly attributed to the enlargement of the average crystal size within the single domain region coupled with the removal of the superparamagnetic fraction in the ferrite powders.