La0.8-xGd0.2MgxNi3.1Co0.3Al0.1 (x = 0.1-0.5) hydrogen storage alloys are prepared by an induction melting followed by annealing treatment for 168 h at 1173 K in a sealed stainless steel tube. Instrumentation analyses indicate that the chemical composition and crystalline phase structure of these annealed alloys closely depended on the Mg content (x). At lower x than 0.25, the main phase is the Ce2Ni7-type phase and its phase abundance is 93.4 wt.%. When x > 0.2, the alloys are composed three phases, A(2)B(7)-type, CaCu5-type and PuNi3-type structure, in which phase abundance of the PuNi3- and CaCu5-type phase increases to 44.99 wt.% and 44.8 wt.% respectively. When Mg is controlled at x < 03, the volume of unit cell of Ce2Ni7-type decreases from 0.5391 nm(3) to 0.5170 nm(3). Hydrogen absorption capacity reaches maximum value (1.43 wt.%) at Mg = 0.15, whereas the absorption of hydrogen storage content decreases with the x increase, accordingly. Electrochemical measurements indicates La0.65Gd0.2Mg0.15Ni3.1Co0.3Al0.1 alloy electrode exhibits the maximum electrochemical discharge capacity of 391.4 mAh g(-1) and the best cyclic stability S-100 of 92.0%. (C) 2013 Elsevier B.V. All rights reserved.