To develop the magneto dielectric materials for 915 MHz RFID antenna miniaturization application, the solid state reaction sintering method was adopted to investigate the influences of H3BO3 addition on the microstructure and magneto dielectric properties of the (Ba0.5Sr0.5)3Co2Fe24O41 ferrite. It was found that H3BO3 addition could promote crystallization of the Co2Z ferrites under relatively low sintering temperature. 〖HJ*4/9〗Meanwhile, H3BO3 also suppressed grain growth of the ferrites. With the increase of H3BO3 content, the permeability continuously decreased, while the dielectric constant first increased and then decreased. With 4% H3BO3 addition, the material could obtain the magneto dielectric properties with a permeability of 2.45, a dielectric constant of 10.41, and a magnetic loss tangent of 0.057 and a dielectric loss tangent of 0.005 at 915 MHz.