A numerical investigation is performed into the heat transfer performance and entropy generation of natural convection in a partially-heated wavy-wall square cavity filled with Al2O3-water nanofluid. The simulations focus specifically on the effects of the nanoparticle volume fraction, the Rayleigh number and the wavy-surface geometry parameters on the mean Nusselt number, total entropy generation and Bejan number. The results show that the mean Nusselt number increases and the total entropy generation decreases as the volume fraction of Al2O3 nanoparticles increases. By contrast, the mean Nusselt number reduces and the total entropy generation increases as the amplitude and wavelength of the wavy-surface increase. Moreover, the Bejan number increases with an increasing amplitude and increasing wavelength of the wavy-surface. Finally, for all values of the Rayleigh number, the Nusselt number increases and the entropy generation reduces as the peak in the wavy surface approaches the horizontal center-plane of the cavity. Overall, the results presented in this study provide a useful source of reference for enhancing the natural convection heat transfer performance in partially-heated wavy-wall cavities while simultaneously reducing the entropy generation. (C) 2014 Elsevier Ltd. All rights reserved.