A series of numerical simulations of fluid flow and heat transfer based on two-dimensional unsteady model of MHD thermal convection have been performed. The computational domain is a rectangular cavity with an aspect ratio of 2, filled with electrically conductive fluids at different Prandtl numbers. The process medium is assumed to be subjected to DC heating by a pair of plate electrodes located at the cavity sidewalls. The top and bottom walls are assumed to be electrically insulated. The upper boundary of the cavity is cooled by the atmosphere and all the other walls are kept thermally insulated. For Pr = 1 and Pr = 0.1 fluid, the simulation results show that the fluid flow and heat transfer rate become time independent and reach steady-state conditions. On the contrary, for Pr = 0.01 fluid, it is found that physically realizable periodic oscillation flow evolves, significantly affecting the heat transfer. These transient characteristics of velocity and temperature fields are presented graphically. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.