A soft hexagonal ferrite sintered material includes crystal particles of M-type hexagonal ferrite corresponding to a general chemical formula MFe₁₂O₁₉ wherein M is at least one element selected from the group consisting of Ba, Sr and Pb. Crystal particles having particle diameters of 5 m to 100 m are extracted from a sintered material produced from a precursor powder mixture. The extracted particles as seed crystals are mixed with a calcined powder comprising fine crystals having the above composition and particle diameters of 0.5 m to 3 m, then is sintered until the intended particle growth of the crystal particles in the sintered material is achieved to give an average particle diameter of 30 m to 500 m.