The opportunity of compounds in catalyst to adsorb the hydrogen was studied. The adsorption capability of catalysts was studied within temperature interval 200-350-5000C. The probable mechanism of water catalytic decomposition has been worked out on the base of catalysts testing carried out by roentgen-phase analysis. The spines as NiAl2O4, FeAl2O4 and Fe0, Ni0 are formated during the preparation of catalyst in low pressure condition (Рdiff.=10-15mmHg). The process of water decomposition to hydrogen and oxygen goes on in the presence of Fe0. Approximately 35% of produced hydrogen spent on formation of intrusion hydrides and 65% of hydrogen is in produced gas. The opportunity of compounds in catalyst to adsorb the hydrogen was studied. The adsorption capability of catalysts was studied within temperature interval 200-350-5000C. Due to oxidation of Fe0 to Fe2O3 activity of catalyst in water decomposition reaction gets down. Formation of FeAl2O4 also restricts catalysts activity because of active component of catalyst became be blocked. Decrease of specific density of Ni-Al2O3; Fe-Al2O3 goes on due to increasing the volume after intrusion of hydrogen into the crystal lattice of catalyst. Increasing of specific density of γ-Al2O3 goes on due to adsorption of hydrogen. Increasing of Ni-Fe-Al2O3 catalysts specific density after water decomposition (0.968 g/sm3) in comparison with catalysts treated with hydrogen (0.860 g/sm3) is explained with Fe2O3 formation. Parameters of crystal lattice and volume of elementary cell were calculated. The probable mechanism of water catalytic decomposition has been prepared on the base of catalysts testing carried out by rentgen-phase analyses.