A new LaMg4Cu intermetallic compound with hexagonal UCoAl4 type structure is prepared by induction melting and subsequent heating treatment. The compound rapidly absorb 3.3 wt% hydrogen at 573 K under 4.0 MPa H2 for the first cycle, leading to phase segregation into LaH3, MgH2 and MgCu2. The reversible dehydrogenation capacity is 2.6 wt% at 523 K, forming a mixture of LaH2, Mg and Mg2Cu. The PCT curves show two plateaus corresponding to the formation of Mg and Mg2Cu, respectively. Compared with mechanically manufactured Mg and bulk Mg2Cu alloy, our in-situ generated LaH2, Mg and Mg2Cu mixture exhibits excellent kinetics and cycling properties, which is mainly attributed to the La-Mg-Cu-H nanostructures via the hydrogen-induced decomposition of LaMg4Cu intermetallic compounds.