This paper analyzes heat transfer and fluid flow of natural convection in inclined cavity filled with CuO-water nanofluid heated from one side and cooled from the ceiling. The transport equations for the flow are solved numerically by the finite volume element method using the SIMPLER algorithm Based on numerical predictions. The effects of Rayleigh number and aspect ratio on flow pattern and energy transport are investigated for Rayleigh numbers ranging from 10(4) to 10(7) volume fraction of solid varied to 0%-4% and for five different aspect ratios of 0.08, 0.1, 0.125, 0.25 and 0.5. It is found that the effect of Rayleigh number on heat transfer is less significant when the enclosure is shallow (AR = 0.5) and the influence of aspect ratio is stronger when the enclosure is tall and the Rayleigh number is high. The subject of this paper is to study the effect of Rayleigh number on the nanofluid flow inside the enclosure and the effect of nanoparticles on heat transfer. Copyright (C) 2014, The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications, LLC.