The mechanochemical milling of Mg and Mg_2Ni alloys were carried out to examine the enhancement of hydrogen storage properties of Mg alloys. The hydroge characteristics of the ball-milled products were evaluated with a Sievert-type apparatus and electrochemical test. Various intermediate compounds were obtained by chemical reactions induced during the ball milling of Mg of Mg_2Ni alloys with C, Ni, Ni_2Cl and Ca_2Cl. The system of Mg_2Ni with 10 wt% C improved markedly the kinetics of hydrogen absorption, while the hydrogen capacities were practically unchanged. The hydrogen storage alloys such as Mg-Ca can be successfully.