Z-type hexaferrites in series (Ba 0.5 Sr 0.5 ) 3 Co 2 Fe 22−x Al x O 38 +1.0wt% H 3 BO 3 (where x=0.0, 0.4, 0.8, 1.2, 1.6, 2.0, and 2.4) were prepared by a conventional ceramic technique. Aluminum substitution iron has been used to enhance sintering density and direct current (DC) resistivity, and decrease magneto-dielectric losses of the ferrites. Meanwhile H 3 BO 3 addition has been used to lower sintering temperature, reduce permeability and enhance resonance frequency. A second phase of Al 4 B 2 O 9 was found in the XRD patterns (where x=2.0, 2.4). The replacement of Fe 3+ ions by Al 3+ ions promoted sintering and increased density of the ferrites, which resulted in the increase of real permittivity. Comparatively, a ferrite sample with x=1.6 presented the best performances in terms of densification, microstructure, magneto-dielectric property, and loss tangent. Since loss tangent was kept low with the frequency ranging from 10MHz to 1.2GHz, such magneto-dielectric material could be used in this frequency range for antenna miniaturization.