The LaNi3.8Al1.0Mn0.2 hydrogen storage alloy annealed at different temperatures (T=1173K, 1223K, 1273K, 1323K) was investigated to examine the effect of annealing temperature on the crystal structure, activation and hydrogen absorption/desorption performance. It was found that the non-CaCu5 phases became more tiny and dispersive after annealing. All the alloys consisted of the same matrix phase with CaCu5 type structure. Although it was harder to activate the annealed alloy than the as-cast alloy, the activation became easier with the increase of annealing temperature for the annealed alloy. The plateau pressure was decreased at first with the increase of annealing temperature when T≤1223K and then increased. Changes in both the lattice strain and the degree of Sf in the alloys showed the same trend with that of the annealing temperature, exhibiting a maximum at T=1223K. . It was also found that the absolute value of the enthalpy was increased with the increase of annealing temperature when T≤1223K and then decreased, showing the same change trend as that of the cell volume. Moreover, the pulverization resistance and kinetics of the alloy were improved by annealing. The pulverization resistance was weakened at first with the increase of annealing temperature when T≤1223K and then increased, but the kinetics of the alloy was almost not influenced by the annealing temperature.