The object of this study is to enhance the dispersion frequency of Z type Magnetoplum-bite ferrite with the composition of 2CoO⋅3BaO⋅12Fe₂O₃. Firstly, the substitution of of strontium ions with smaller ionic radius for some of barium ions in the formula 2CoO⋅(Ba_1-xSr_x)O⋅12Fe₂O₃ leads to the maximum value of μQ when x is 0.5. Secondly, when the iron content is shifted from stoichiometric value and hot-pressed in air or in an oxygen atmosphere in keeping x = 0.5, the sample with the composition 2CoO⋅3(Ba_0.5 Sr_0.5)O⋅10.8Fe₂O₃ revealed the best μQ value, especially for the sample hot-pressed in the oxygen atmosphere. Its resonance frequency corresponding to μ″ maximum extended to 2.5 GHz, which is sufficiently larger than the value of 1.4 GHz previously reported.