Nanofluids, containing metal or nonmetal particles with nanometer sizes, exhibit much greater thermal conductivity than predictions. It has been proposed that interfacial structures formed by liquid molecule layering might play role. We investigated the impact of this interfacial nanolayer on the effective thermal conductivity of nanofluid. An expression for calculating enhanced thermal conductivity of nanofluid has been derived from the general solution of heat conduction equation in spherical coordinates and the equivalent hard sphere fluid model representing the microstructure of particle/liquid mixtures. The effects of nanolayer thickness, nanoparticle size, volume fraction, and thermal conductivity ratio of particle to fluid have been discussed. The predicted results are in good agreement with some recent available experimental data. (c) 2005 Elsevier Ltd. All rights reserved.