In this paper, we studied the substitution of Fe in BaFe12O19 by Mn. The main results are as follows: (1) For polycrystalline materials of composition BaFe12-xMnxO19, the amount of maximum substitution of Mn is x=4, and the valence of Mn ions are mostly 3+. (2) Mn ions enter only 12 k and 2 a sites, and noncolinear spin structure appears with higher content of Mn (3) The saturation magnetization σ, the anisotropy constant k1 and the Curie temperatur Tc decreas with the increase of Mn content. (4) The zero field splitting constant Dh of Mn in M-type hexagonal structure is lower then that in garnet structure.