Abstract The hydrogen absorption of the M5X3 phase ZrAl compounds was studied. The compounds exist in two forms: a high temperature phase with D8m W5Si3 structure and a Nowotny phase of D88 Mn5Si3 structure stabilized by the presence of oxygen. Zr5Al3 with the D8m structure absorbs hydrogen at room temperature and at a hydrogen pressure below 1 atm. The hydride Zr5Al3H8 is formed at a hydrogen pressure of 1 atm. More than two hydrogen atoms can be desorbed on temperature cycling up to 200 °C. The structure of the hydride was determined by powder diffraction to be monoclinic ( a = 11.072 A , b = 11.072 A , c = 5.890 A , β = 90.57°, body centred). Zr5Al3 forms the hexagonal D88 Zr5Al3O1−x structure when oxygen is present. A hexagonal supercell with an a axis 3 1 2 times larger than that of the parent D88 structure appears for an oxygen content above Zr5Al3O0.1. Unlike previously studied D88 structures, such as Y5Si3 and Ho5Si3, which are poisoned for hydrogen absorption when oxygen is included, this oxygenstabilized D88 system still exhibits significant reversible hydrogen absorption. That this structure retains its hydrogen absorption capacity is not consistent with previous assumptions that the hydrogen and oxygen exclusively occupy the characteristic metal octahedral columns.