A method of separating hydrogen from mixture with at least one gas selected from the group consisting of methane and its higher homologs, nitrogen, noble gases, CO, CO.sub.2, O.sub.2, NH.sub.3, H.sub.2 O, and H.sub.2 S, comprising contacting the mixture with active magnesium thereby selectively to absorb the hydrogen by forming magnesium hydride, separating the unabsorbed gas from the magnesium hydride, heating the magnesium hydride thereby to desorb the hydrogen in purified form and regenerate active magnesium from the hydride, and recovering the desorbed hydrogen.