This study investigated the non-equilibrium hydrogen absorption reaction paths of the AB(5)-type LaNi2Co3 alloy using time-resolved in situ synchrotron X-ray diffraction. Diffraction data were collected every second for reactions under two hydrogen loading pressures. Hydrogen absorption with a hydrogen loading of 1 MPa rapidly transformed alpha phase to a transient phase (estimated to be LaNi2Co3H3.1-3.6, named gamma*); this has not previously been observed under equilibrium processes. The gamma* phase continuously transformed into the gamma phase (LaNi2Co3H4.5-5.0), and the beta phase (LaNi 2Co3H similar to 36) was not formed. When 0.18 MPa of hydrogen was loaded, initially, the gamma* phase appeared, followed by the formation of the beta phase, finally transforming into the gamma phase. These results indicate that a higher loading pressure promotes the formation of the gamma* phase and assists its continuous transformation into the y phase by enhancing the dissolution of hydrogen into the alpha and gamma* phases. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.