PdCuAu alloy thin films were prepared by co-electrodeposition over a large composition range ([Pd] = 14-74 at.%, [Cu] = 2-82 at.%, [Au] = 0-66 at.%) and then annealed at 400 degrees C. The influence of the alloy composition and annealing treatment on the crystalline structure, film morphology and hydrogen solubility (at room temperature) of the various PdCuAu alloys was investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical method, respectively. All the as-deposited samples displayed a monophased face-centered-cubic (fcc) structure. After annealing, a face-centered-cubic to body-centered-cubic (bcc) phase transition was observed. Thanks to the stabilizing effect of Au on the bcc structure this phase transition occurs over a large composition range. The hydrogen solubility increased with the Pd content in the alloy and with the Au content at a constant Pd concentration. The fcc to bcc phase transformation resulted in a major decrease of the hydrogen solubility in the alloy. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.