In this paper, we have proposed a theoretical analysis to investigate buoyancy driven convection of nano-fluids in an infinitely long channel under superimposed magnetic field. We derive closed form analytical solutions for the magnetohydrodynamic flow and temperature field under two distinctive wall boundary conditions. Proceeding further ahead, we also present an analysis for the total entropy generation due to magnetohydrodynamic fluid friction and heat transfer irreversibilities. Utilizing water based Al2O3 nanofluids, results are shown for the following range of conditions as 0 <= Ha <= 50, 0 <= phi <= 4% and 10(3) <= Gr <= 10(5). It is revealed that magnetohydrodynamic effect reduces flow strength. Likewise the case of the velocity profiles, magnetic effect reduces the magnitude of temperature distribution. Total entropy generation shows decreasing trend when the volume fraction of the nanofluids is increased. Increasing nanoparticle size results in increasing total entropy generation and the Bejan number. (C) 2013 Elsevier Ltd. All rights reserved.