Recently, our group found a new phase with a composition close to LaCuMg8. This compound crystallizes in the La2Mg17 structure type. A similar hydrogen sorption behavior was observed for both La2Mg17 and LaCuMg8 compounds with a two steps mechanism. During the first step, LaCuMg8 absorbs around 3wt% with a low kinetic; the decomposition into LaH3, MgH2 and Cu2Mg is also observed. This first step is considered as the activation process. The second step consists in the reversible desorption/absorption of hydrogen by magnesium and also the reversible transformation of Mg2Cu into MgCu2. In order to improve the activation process, the influence of ball milling and cold rolling was tested. LaCuMg8 can not be synthesized by ball milling starting from elemental powders (LaCu + 8Mg). However, cold rolling on as-cast LaCuMg8 compound improves the activation. Indeed, more than 3%wt is absorbed after 1 hour which is 20 times faster than LaCuMg8 as cast. An effect of CuMg2, induced by cold rolling was proposed.