The composite materials La2Mg17-xwt% LaNi5 have been synthesized with various values of x, and the hydrogenation behaviour of these materials has been extensively studied. The as-synthesized materials were activated by heating the materials at about 360 +/- 10 degrees C temperature under a hydrogen pressure of 33 kg cm(-2) for nearly 6 h. The maximum hydrogen storage capacity was found to be 5.3 wt % for the composite material La2Mg17-10 Wt % LaNi5 at 400 +/- 10 degrees C temperature. This is one of the very highest storage capacities known so far. The initial rate of hydrogen absorption of La2Mg17-10 Wt % LaNi5 was found to be 20 cm(3) g(-1) min(-1) (at 400 +/- 10 degrees C temperature). In order to elucidate the influence of LaNi5 addition, which significantly accelerated the hydriding rate and hydrogen storage capacity of La2Mg17, structural-microstructural characterization and chemical analysis of the composite materials employing X-ray diffraction, scanning electron microscopy and energy dispersive analysis of X-rays techniques have been carried out.