Magnetite was modified by reaction with alkaline solution containing Co2+ and Fe2+ to obtain a cobalt ferrite layer on the surface of particles.The influences of modification conditions on the properties were investigated.The as-prepared particles were characterized by X-ray diffraction(XRD)and transmission electron microscope(TEM).The results show that pH value influences the particles composition directly,the desirable CoFe2O4 is obtained as pH value is 12.The coercivity of particles increases with the increase of cobalt content,and the cobalt efficiency reaches a maximum value at cobalt content of 2.71%(mass fraction).With cobalt modification,the magnetite particles have the similar lattice constant and structure to that without cobalt modification,and the squareness ratio is almost 0.5.The increase of the coercivity is attributed to the uniaxial magnetic anisotropy and magnetocrystalline anisotropy of cobalt-ferrite itself.