Ultrafast laser experiments were used to study electron-phonon coupling in Au nanoparticles in the 2.5 to 8 nm size range in aqueous solution. The electron-phonon coupling constants for these samples were found to be independent of the particle size. This is attributed to a weak interaction between the electron gas and the surface phonon modes in Au. Calculations were performed which show that the coupling between the hot electrons and the surface accounts for less than 10% of the total electron energy losses for these particles. Thus, bulk electron-phonon coupling dominates the relaxation of excited electrons in Au particles, for particles as small as several hundred atoms. (C) 2000 American Institute of Physics. [S0021-9606(00)70813-0].