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A systematic study on the phase formation and magnetic properties of M‐type hexagonal ferrite solid solutions Sr1−xLnxFe12O19 with rare‐earth ions Ln=Pr, Nd, Sm, Eu, and Gd was performed. All ferrite samples were prepared by the mixed oxide route and characterized with a combination of powder XRD, microscopy, electron‐probe microanalysis, and thermal analysis. For Ln=Pr, Nd, and Sm, the formation of M‐type ferrite solid solutions with limited solubility of rare earths was observed. The lattice parameters of Sr1−xLnxFe12O19 exhibit a linear variation with x within the range of ferrite solid solution, i.e., c0 decreases with x. For Eu‐ and Gd‐containing samples substituted X‐type ferrites are observed. The solubility limits of the rare‐earth ions within the M‐type ferrite lattice range from x=0.46 for Pr to about x=0.17 for Sm. Eu and Gd can be substituted to lesser amounts in the X‐type ferrites. The saturation magnetization at T=5 K increases with increasing rare‐earth concentration for Pr, Nd, and Sm. Mössbauer spectrometry reveals signals originating from Fe3+ on five different crystallographic positions of the M‐type structure as well as ferrous ions on Fe 2a sites. The spectra of the hexagonal ferrites with different rare‐earth ions (La, Pr, Nd, Sm) are very similar and show systematic variations of the hyperfine fields with rare‐earth concentrations.