Cobalt-Zine ferrite is known for its chemical stability and composition-sensitive demagnetization temperature. In this work, Co xZn1-xFe2O4 nanocrystals have been synthesized by conventional and size-controlled coprecipitation methods. The effect of Co2+ atomic fraction, 'x', on the magnetic properties of nanocrystals was investigated. The average crystallite size of the ferrite nanocrystals synthesized by conventional co-precipitation ranged between 8.8 nm and 13.6 nm for 'x' between 0.5 and 1.0, respectively. The corresponding maximum magnetization varied from 24emu/g to 60emu/g. The coercivity value was increased by a rising 'x' or by producing the nanocrystals under size-controlled synthesis conditions. This increase in coercivity was attributed to both. an increase in the magnetic anisotropy energy and the promotion of crystal growth within the single domain region. As expected, the demagnetization temperature was strongly dependent on the ferrite composition.