Recent measurements have demonstrated that nanofluids exhibit much higher thermal conductivity than predictions by traditional models. Here we developed a model for calculating the enhanced thermal conductivity of nanofluids, which includes the impact of interfacial nanolayers formed by liquid molecule layering on the particle/liquid interfaces. The effective thermal conductivity is 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.