Adjusting the rare earth (RE) compositions in the RE–Mg–Ni alloys can effectively improve the electrochemical hydrogen storage performances of the alloy electrodes. Herein, A 5 B 19 type hydrogen storage alloys with the elemental composition of La 3 RMgNi 19 (R = La, Pr, Nd, Sm, Gd and Y) were prepared by induction melting and subsequent annealing. The phase transformation and electrochemical hydrogen storage performances of La 3 RMgNi 19 alloys were investigated in detail. X-ray diffraction analysis shows that La 3 RMgNi 19 alloys contains AB 5 , A 2 B 7 (Ce 2 Ni 7 and Gd 2 Co 7 ) and A 5 B 19 (Pr 5 Co 19 and Ce 5 Co 19 ) phases, and the increase of annealing temperature obviously reduces the phase abundance of LaNi 5 phase. Sm, Gd and Y contribute to the formation of A 5 B 19 phase, especially Ce 5 Co 19 , and Pr and Nd promote the formation of A 2 B 7 phase for La 3 RMgNi 19 alloys. With increasing annealing temperature, the maximum discharge capacity ( C max ) of La 3 RMgNi 19 alloy electrodes first increases and then decreases, and the highest value of C max is achieved as the annealing temperature is 1223 K. This evolution trend of the C max is inversely proportional to that of LaNi 5 phase abundance. The substation of La by Pr, Nd, Sm, Gd or Y causes the decrease of C max , which is mainly ascribed to the decrease of cell volume. Due to the decrement of LaNi 5 phase, the cycling stability increases at first when the annealing temperature is below 1223 K. However, when annealing temperate further increases to 1273 K, the cycling stability decreases, which is caused by the increment of LaNi 5 phase. It is worth noting that the phase composition (LaNi 5 phase abundance) plays more important role than other factor. The slight decrement of high-rate dischargeability resulted from the substitution of La by Pr, Nd, Sm, Gd or Y should be attributed to the combined effect of advantageous and disadvantageous factors. [ABSTRACT FROM AUTHOR]