Gadolinium nanoparticles, deposited via an inert gas evaporation method, show improved stability towards oxidation and it is therefore possible to carry out an ex-situ investigation on "bare" Gd nanoparticles, i.e., in the absence of a protective Pd layer, for the first time. A size-induced structural transformation from hexagonal close packing to the higher-symmetry face-centered cubic structure is observed. The important observation of hydrogen-Gd-nanoparticle interaction at room temperature and atmospheric pressure, without a Pd catalytic layer, makes Gd nanoparticles a potential candidate for hydrogen-sensing, switching, and storage applications.