In this numerical work, natural convection of CuO-water nanofluid and pure water in a cavity submitted to different heating modes on its vertical walls, is analyzed using the Lattice Boltzmann Method (LBM). The effective thermal conductivity and viscosity of nanofluid are calculated by KKL (Koo-Kleinstreuer-Li) correlation. The influence of pertinent parameters such as Rayleigh number (Ra = 10(3)-10(6)), Hartmann number (Ha = 0-80), heat generation or absorption coefficient (q = -10, -5, 0, 5, 10) and nanoparticle volume concentration (phi = 0-0.04) on the flow and heat transfer characteristics has been examined. In general, by considering the role of Brownian motion, the enhancement in heat transfer is observed at any Hartman and Rayleigh numbers. In addition, the heat generation or absorption influences the heat transfer in the cavity at Ra = 10(3) more than other Rayleigh numbers as the least effect is observed at Ra = 10(6). (C) 2016 Elsevier B.V. All rights reserved.