Abstract The pressure–composition–temperature relations and the reaction kinetics for the NdNi 5− s Sn s ( s=0, 0.1, 0.2, 0.4)–H 2 system are measured at temperatures between 253 and 293 K. The PCT for NdNi 5, which presents two well-separated plateau regions at rather high pressures, is strongly altered by the Sn-substitution. Namely, both plateau pressures are continually reduced with increasing substitution and the relative separation is reduced to cause a nearly single sloped plateau without reducing the maximum hydrogen capacity appreciably (H/M∼1.0). Furthermore, the hydriding and dehydriding kinetics are substantially improved by the Sn-substitution. The promotion of the reaction kinetics is related with increased tendency toward pulverization during hydriding–dehydriding cycles. X-ray diffraction study suggests that NdNi 5 is structurally stabilized by the Sn-substitution against decomposition during the H–D cycles. In conclusion, NdNi 4.8Sn 0.2 appears to be favorable for use as a hydrogen storage alloy in the above temperature range.