A systematic study on the phase formation and magnetic properties of M-type hexagonal ferrite solid solutions Sr(1-x)Ln(x)Fe(12)O(19) 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 Sr(1-)xLn(x)Fe(12)O(19) exhibit a linear variation with x within the range of ferrite solid solution, i.e., c(0) 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. Mossbauer 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.