The study of nanoparticles has generated great interest in recent years in several areas of research. For example, in multiferroic composite materials, the combination of ferroelectric materials and ferrites may lead to magnetoelectric effect. In particular, CoFe2O4 and NiFe2O4 combined/fused/?? as magnetic phase is of interest, as these materials are isolating oxides with high transition temperatures and high saturation magnetization. In this work, the effective magnetic anisotropy was studied as a function of the temperature for nanocrystalline nickel doped cobalt ferrite samples NixCox-1Fe2O4., x = 0,0; 0,25; 0,50 and 1).