Studies were undertaken of phase transitions of iron oxide obtained from iron oxide-hydroxides of type co-, 13-, y-and 5-FeOOH, and used as a support of ruthenium catalysts Ru/Fo203, employed in the water-gas shit~ reaction. In asprepared pure supports and ruthenium catalysts the main phase was r Alter use in the water-gas shill reaction, the support showed the presence of different phases of iron oxide. The most active Ru/~0203 catalysts prepared on the basis of cz-and 5-FeOOH, after use in the water-gas shift reaction, revealed the presence of Fe304 or a mixture of phases Fe304 and y-Fo203. The least active catalysts, prepared on the basis of 13-and y-FeOOH, contained a solid solution of Fe304-y-F0203 with traces of cr