The high temperature deformation behaviors of Ti-6Al-4V alloy and the alloy hydrogenated with 0.3 wt%H were studied. Comparing with the unhydrogenated alloy, the hydrogenated alloy exhibited higher plasticity and lower flow stress. The possibilities of hydrogen-induced plasticity were attributed to the effect of hydrogen on dislocation density, stacking fault energy in starting microstructure and dislocation mobility, dynamic recrystallization during high temperature deformation. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.