Inelastic X-ray scattering was measured for copper/ethylene glycol nanofluid at 298 K. The collective excitation of the solvent was analyzed by a generalized Langevin equation. The thermal diffusion coefficient and mu(fast)-and a(structure)-relaxations of the solvent for the nanofluid are larger and faster than those of pure liquid, respectively. The high-frequency sound velocity obtained from momentum transfer dependence of a maximum in the longitudinal current-current correlation function increases with increasing the number of copper nanoparticles. The enhanced thermal conductivity of copper/ethylene glycol nanofluid could be related to the solvent dynamics.