Hydrogen embrittlement in metals is a challenging technical issue in the proper use of hydrogen energy. Despite extensive investigations, the underlying mechanism has not been clearly understood. Using atomistic simulations, we focused on the hydrogen embrittlement in vanadium-based hydrogen separation membrane. We found that, contrary to the conventional reasoning for the embrittlement of vanadium, the hydrogen-enhanced localized plasticity (HELP) mechanism is the most promising mechanism. Hydrogen enhances the nucleation of dislocations near the crack tip, which leads to the localized plasticity, and eventually enhances the void nucleation that leads to the failure. Those results provide an insight into the complex atomic scale process of hydrogen embrittlement in vanadium and also help us design a new alloy for hydrogen separation membranes. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.