Hydrogen storage alloys Mg(2)Ni and Mg(2)NiH(4) were synthesized at below 733 K by the process HCS. The product was examined by X-Ray diffraction and hydriding/dehydriding dynamics was tested. The result reveals that (1) High pure products of Mg(2)Ni and Mg(2)NiH(4) can be obtained even at temperature 673 K and 0. 1 MPa argon and 1.0 MPa hydrogen, respectively; (2) Both products are high active absorbing hydrogen > 3.2 mass % at 603 K without activation process. The result is very attractive due to the low temperature and pressure for the production of hydrogen storage alloys.