The  catalytic effect of titanium on  the hydrogen sorption properties of a Mg–Y–Ti alloy has been inves- tigated. The  alloy is formed by  a majority phase Mg24+x Y5 , a minor phase of solid solution of Y in Mg and Ti clusters randomly dispersed in  the sample. During the ?rst hydrogen absorption cycle 5.6 wt.% hydrogen was absorbed at temperatures above 613 K. The alloy decomposed almost completely to MgH2 and YH3 . After hydrogen desorption pure Mg and YH2    were formed. For further absorption/desorption cycles the material had a reversible hydrogen capacity of 4.8 wt.%. The  MgH2 decomposition enthalpy was determined to −68 kJ/mol H  , and the calculated activation energy of hydrogen desorption of MgH２.