This study examined numerically the natural convection induced by a temperature difference between a cold outer inclined square enclosure and a hot inner circular cylinder. A two-dimensional solution for natural convection was obtained using the finite volume method with second-order accuracy and the immersed boundary method to handle efficiently the inner circular cylinder within an inclined square enclosure. The present study considered the effects of the following parameters on fluid flow and heat transfer in an enclosure: Rayleigh number from 10(3) to 10(6), the dimensionless cylinder radii from 0.1 to 0.3 and tilted angle of the enclosure from 0 degrees to 45 degrees. The results showed that the distribution of isotherms, streamlines, local and surface-averaged Nusselt numbers are determined by the combined effects of convection and the distance between the cylinder and walls of the enclosure, which are a function of the Rayleigh number, dimensionless cylinder radius and tilted angle of the enclosure. (C) 2013 Elsevier Ltd. All rights reserved.