We study interactions in LaNi5 − x Al x –H2 (x = 0, 0.2, 0.4, 0.6, and 0.8) systems by the methods of differential thermal and X-ray phase diffraction analyses within the temperature range from the room temperature to 920°C in hydrogen whose initial pressure can be as high as 5.7 MPa. In LaNi5 − x Al x –H2 systems with x = 0, 0.2, and 0.4, the processes of formation and decomposition of the intermetallic hydride run without changes in its symmetry. The process of heating of LaNi5 − x Al x (x = 0, 0.2, and 0.4) alloys in hydrogen results in their homogenization. Thus, the process of heating of the LaNi4.4Al0.6 alloy in hydrogen to 700°C for an initial pressure of about 5.7 MPa results in a partial decomposition (disproportionation) of the original phase accompanied by the formation of lanthanum hydride and Ni3Al. As a result of heating to 575°C in hydrogen ( $$P_{{\text{H}}_{\text{2}} }$$ ≈ 5.0 MPa), the LaNi4.2Al0.8 compound disproportionates into Ni3Al and an unknown phase. After heating to 840°C followed by holding for 1.5 h, we detect the original phase, lanthanum hydride, Ni3Al, and an unknown phase. At the same time, as a result of heating to 910°C followed by holding for 2 h, we observe the formation of a hydride of the original phase with doubled spacing c, lanthanum hydride, and Ni3Al.