Amorphous Mg-x(LaNi3)(100-x) (x = 40, 50, 60, 70) alloys with ribbon shape (5 mm wide, 0.2 mm thick) have been prepared by rapid solidification, using a melt-spinning technique. Their microstructure, hydrogen storage properties and thermal stability were studied by means of XRD, SEM, PCTPro2000 and DSC analysis, respectively. The results indicated that when Mg-x(LaNi3)(100-x) alloys have been hydrogenated at 573 K under 2 MPa hydrogen pressure, LaH3 phase is formed in the case of x (x = 40, 50, 60, 70), Mg2NiH4 phase formed in the case of x (x = 40, 50, 60, 70), Mg2NiH0.3 phase formed in the case of x (x = 40, 50), and MgH2 phase formed in the case of x = 70. Experimental data of hydrogen desorption kinetics, tested at 523 K, 573 K and 623 K, are in good agreement with Avrami-Erofeev equation. The maximum hydrogen absorption capacity is 2.71 wt.% for Mg-70(LaNi3)(30) and 2.35 wt.% for Mg-70(LaNi3)(30), the increase of hydrogen desorption capacity is in the order of x = 70 > x = 60 > x = 50 > x = 40. Based on DSC analysis, the activation energies for dehydrogenation of these samples are calculated to be 122 +/- 2 kJ/mol (x = 40) > 101 +/- 3 kJ/mol (x = 50) > 84 +/- 5 kJ/mol (x = 60) > 64 +/- 3 kJ/mol (x = 70), which are in agreement with the results of hydrogen desorption kinetics. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.