The influence of hydrogen content on the formation of nanocrocrystalline (NC) structure in the Ti-6.3-Al-3.5Mo-1.7Zr wt% alloy during thermal processing, (a+beta)-region deformation and low-temperature vacuum annealing has been investigated. it is shown that the role of hydrogen during alloying of titanium alloys is not reduced only to the effects of hydrogen-induced softening at hot deformation. Hydrogen alloying exerts a significant influence on initial microstructure, phase composition and contributes to the formation of NC structures in titanium alloys resulting from SPD and following hydrogen removal. The grain sizes of 20-30 nm have been produced in workpieces of this alloy. Mechanical properties of NC titanium alloy at room and elevated temperatures have been studied. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.