The effect of hydrogen on hot deformation behaviors of Ti-47Al alloys was studied using a hot simulator. The optimized deformation temperature for Ti-47Al alloys was 1150 degrees C. Flow stress and peak stress were reduced with increasing addition of hydrogen. Peak stress can be reduced by about 33.3% with 1% hydrogen addition at 1150 degrees C and strain rate of 1 x 10(-2) s(-1). There were less dislocation tangles and more twinning and stacking faults in the hydrogenated alloys compared with the unhydrogenated alloys. The hydrogen-induced decrease of flow stress was attributed to hydrogen-induced dislocation mobility and hydrogen-promoted dynamic recrystallization and twinning. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.