The particles of Zn0.2Fe2.8O4, ferrite are prepared by chemical Co-precipitation. The shape of particles are nearly spherical and their mean diameter is about 300?. Epitaxial cobalt ferrite layer is coated on their surface. Coercivity Hc and ferromagnetic resonance line width △H are measured. According to, experimental results, the effective mangnetic anisotropy constant Ku is about 5×105 erg/cm2. That is induced by interface interaction between the inner core of Zn0.2Fe2.8O4 and Co-Fe epitaxial layer. The distance of interaction is about the total thickness of two oxygen ion layers.