Abstract The structure of sputter-deposited Fe⧸Ti multilayers with various layer thickness and its change with annealing at elevated temperatures in vacuum and hydrogen atmosphere have been studied using X-ray diffraction and Auger-electron depth profiling techniques. The multilayers exhibit preferred orientations of Fe (110) and Ti (001) lying parallel to the substrates in the as-deposited states. When they are annealed in vacuum at 523–823 K, interlayer mixing takes place to form a supersaturated bcc solid solution and FeTi compound, and the original modulated structure almost disappears. No indication of solid-state amorphization is obtained during annealing. When the multilayers are annealed under 0.2–0.5 MPa H 2 in the same temperature range, the interlayer mixing is strongly suppressed and the original layer structure is almost preserved, although the Ti layers have transformed to those of δ-TiH 2 or β-TiH x depending on the temperature and H 2 pressure. This effect of hydrogenation on stabilizing the structure of Fe⧸Ti multilayers is well accounted for in terms of a calculated free-energy diagram for the Fe-Ti system.