The hydrogenation behaviour and structural characteristics of the R 5Fe 2B 6 (R=Ce, Pr, Nd, Sm, Gd and Tb) borides have been studied in the present work. Hydride formation is accompanied by an anisotropic expansion of the initial trigonal unit cells (Pr 5Co 2B 6 type crystal structure) in the [001] direction only. Heating in hydrogen of the Pr and Nd containing borides results in their disproportionation and the formation of the R-hydride and two compounds, namely R 1.1Fe 4B 4 and R 2B 5. Recombination to form the initial (Pr,Nd) 5Fe 2B 6 borides is observed on vacuum heating of this three phase mixture. The disappearance of additional phases present in the cast material, demonstrates another example of the successful use of the hydrogenation–disproportionation–desorption and recombination process for the homogenisation of a rare earth containing alloy. Under the same conditions, reversible hydrogen absorption–desorption takes place in the case of the corresponding Sm, Gd and Tb compounds indicating an increase of the thermodynamic stability of the borides with increasing atomic number of the R-component. Hydrogen absorption–desorption properties were characterised by means of temperature–pressure analysis and hydrogen differential thermal analysis. An increase in the thermal stability of the R 5Fe 2B 6H x -hydrides with increasing atomic number of the R-component is consistent with the insertion of the hydrogen atoms into the structural slabs consisting of the rare earth atoms only.