MnZn ferrite powder was modified by SrTiO3 sol and then filled into PTFE matrix to form MnZn ferrite/SrTiO3/PTFE composite. The effect of modification and heat-treatment on the electromagnetic property of the composite was investigated. The results revealed that the as-prepared composite possessed high permeability, high permittivity and low loss. The modification and heat-treatment could improve the electromagnetic property of the composites. The frequency dependence of the dielectric property of the composite is accorded with Debye relaxation theory.