The fracture behaviors of non-hydrogenated, hydrogenated and dehydrogenated Ti-6Al-4V alloys were investigated by in-situ tensile test at room temperature. The distributions of stress and strain near the notch of in-situ tensile specimen were calculated using finite element method. Results indicate that hydrogen has an important effect on the fracture behavior of Ti-6Al-4V alloy. Crack initiation sites differ in the specimens treated by various procedures, and they are related to the stress intensity in specimens under different loads. The fracture mode of non-hydrogenated specimen is a ductile fracture by the initiation and coalescence of microvoids. The hydrogenated specimen shows a mixture of intergranular and transgranular brittle fractures. The dehydrogenated specimen is characterized by a mixture of intergranular and transgranular ductile fractures. The transition of fracture mode is attributed to the hydrogen atoms in solid solution and hydrides. Crown Copyright (c) 2009 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.