In this study, natural convection heat transfer of nanofluids in a wavy-wall enclosure is studied while a heated cylinder is located inside the cavity. The governing equations for a simple cavity are studied based on the previous work and changed it to complicated two-phase nanofluid and solved by finite element method (FEM). Because the location on inside cylinder has a significant effect on the heat transfer and Nusselt number, it is important to find the best location for this cylinder. In our study the cylinder is movable in X and Y directions which affects the temperatures, stream lines and nanoparticles concentration contours. The results indicate that center location for the cylinder assists the heat transfer in both wavy side walls. (C) 2016 Elsevier Ltd. All rights reserved.