Abstract: 57Fe Mössbauer spectroscopy, DSC, X-ray diffraction and magnetic measurements have been applied to study the polycrystalline Er2−x Pr x Fe14B (x =0.25, 0.5, 0.75, 1.0, 1.5) and Er2−x Gd x Fe14B (x =0.5, 1.0, 1.5) compounds. A comparison of results obtained for Pr and Gd-based compounds is presented in this paper. Special emphasis was put on the spin reorientation phenomena (change of spin orientation from planar to axial arrangement) occurring in these series. The spin reorientation in each compound has been investigated mainly by narrow step temperature scanning in the neighborhood of the spin reorientation temperature, T SR. Initial magnetization versus temperature measurements allowed to establish the temperature regions of reorientations and also the Curie temperatures of the compounds. The obtained Mössbauer spectra were analyzed by using a procedure of simultaneous fitting and the transmission integral approach. Consistent fits were obtained, T SR and the composition dependencies of hyperfine interaction parameters were derived from fits for all studied compounds. DSC studies proved that the spin reorientations were accompanied by thermal effects. Transformation enthalpy and T SR were determined from these studies only for compounds in which R=Gd. The T SR obtained with different methods were analyzed and the spin arrangement diagrams for two series were compared. [Copyright &y& Elsevier]