The present work deals with the steady-state natural convection in a cubic enclosure filled with the water-Au nanofluid. The enclosure is heated on the vertical and cooled from the adjacent wall, while the other walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The effects of the volume fraction of nanoparticles in the range 0% <= phi <= 5% on the heat transfer characteristics of Au nanofluids are investigated for the nominal values of base-fluid Rayleigh number (10(1) <= Ra-bf <= 10(6)). It is shown that adding nanoparticles in a base-fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the mean Nusselt number (Nu) over bar values for nanofluids (phi > 0%) are smaller than those obtained in the case of pure fluid with the same nominal value of Rayleigh number Rabf due to the weakening of convective transport. (C) 2014 Elsevier Ltd. All rights reserved.