Monodispersed palladium nanoparticles protected with n-octyl isocyanide were prepared, and their hydrogen absorption behavior was evaluated. The formation of the nanoparticles has been confirmed by means of H-1 NMR and elemental analysis. Fourier transform infrared (FT-IR) showed that three distinct bands (2156, 1964, and 1611 cm(-1)) assigned to mono-, double-, and triple-bridged isocyanide ligands on the palladium surface. The average diameter of the particles was estimated to be 2.1 +/- 0.7 nm from observation by transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) analysis revealed that the particles contained Pd(0) with little amounts of Pd(II) or Pd(IV), in sharp contrast to the thiol- or phosphine-stabilized palladium nanoparticles. The absorption and desorption of hydrogen were reversible, and the reactions were much faster for the nanoparticles than for the bulk palladium metal, whereas the storage capacity was almost the same, 0.6 wt %.