The influence of hydrogen uptake on the microstructure and mechanical properties of swaged Gum metal rods was investigated. The Gum metal rod absorbed hydrogen under moderate hydrogen pressure at elevated temperatures. For a hydrogen content (hydrogen to metal ratio H/M) of 0.2 < HIM < 0.4, marked grain refinement was observed, and the strain-to-failure increased beyond that of a swaged specimen while maintaining yield stress and ultimate tensile strength. Since grain refinement was not observed in recrystallized specimens, it was deduced that lattice defects induced during the swaging process play an important role in grain refinement with charged hydrogen. The ductile-to-brittle transition of the fracture mode was observed at H/M > 0.4. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.