To provide a new hydrogen storage alloy having excellent hydrogen releasing characteristic at a low temperature not higher than 200°C and produced at a low material cost, and also to provide a composition and an intermetallic compound containing the alloy.

The new hydrogen storage alloy having excellent hydrogen releasing characteristic at low temperature and low material cost and also the composition and the intermetallic composition each containing this alloy can be provided by utilizing the fact that the intermetallic compound Mg3Ni2Mn1 which exists in the ternary hydrogen storage alloy having a composition consisting of Mg, Ni, Mn and inevitable impurities an also having a composition ratio represented by Mg3+aNi2+bMn1+c (wherein, a=-1 to 1, b=-1 to 2 and c=-0.45 to 2 are satisfied) can occlude/release hydrogen even at a temperature far below 200°C.