The problem of entropy generation in a fluid saturated porous cavity for laminar magnetohydrodynamic natural convection heat transfer is analyzed in this paper. Heat transfer results are also presented additionally. Darcy's law for porous media is considered. Magnetic force is assumed acting along the direction of the gravity force. As boundary conditions of the cavity, two vertical opposite walls are kept at constant but different temperatures and the remaining two walls are kept thermally insulated. For a range of Rayleigh number (Ra = 1-10(4)) and Hartmann number (Ha = 0-10), heat transfer, overall entropy generation rate, and heat transfer irreversibility are presented in terms of dimensionless Nusselt number (Nu), entropy generation number (Ns), and Bejan number (Be), respectively. Finally, parametric results are presented in terms of isothermal lines, streamlines, isentropic lines, and iso-Bejan lines. (C) 2004 Elsevier Ltd. All rights reserved.