Numerical technique is employed to derive a solution to the transient natural convection flow of an incompressible Viscous fluid past an impulsively started semi-infinite isothermal Vertical plate. Heat transfer effects are taken into account and the governing equations are solved using implicit finite-difference method. Transient and steady-state velocity and temperature profiles, the local as well as average skin friction and the Nusselt number are shown graphically. The velocity and temperature profiles at small Values of time t are shown to agree with the exact solution of the flow past an impulsively started infinite vertical isothermal plate. The heat transfer effects of different parameters Pr (the Prandtl number) and Gr (the Grashof number) are discussed. It is observed that the number of time steps for convergence to steady state depends strongly on Gr. (C) 2001 Editions scientifiques et medicales Elsevier SAS.