Entropy generation due to steady state heat transfer and the motion of the vertical boundaries in a two-dimensional square cavity is numerically studied, using the value of the velocity and temperature obtained by solving the Navier-Stokes equation coupled with the energy equation with the finite element method and an operator splitting scheme. Increasing the Richardson number, the entropy generation by fluid friction is intensified inside the cavity due to the vortex formation at the central part of the cavity. The entropy generation by heat transfer becomes more intense at the vertical walls and the central low part of the cavity due to the stronger temperature gradients at this region. (C) 2011 Elsevier Ltd. All rights reserved.