We have investigated the hydrogen absorption behavior of Pd/Pt nanoparticles with a core/shell-type structure. From the results of the hydrogen pressure-composition (PC) isotherm and solid-state H NMR measurements, it was revealed that the Pd/Pt nanoparticles can absorb hydrogen, and most of the absorbed hydrogen atoms are situated around the interfacial region between the Pd core and the Pt shell of the Pd/Pt nanoparticles, indicating that the core/shell boundary plays an important role in the formation of the hydride phase of the Pd/Pt nanoparticles. Copyright © 2008 American Chemical Society. 2