A sliding mode control approach is proposed to stabilize a class of underactuated systems which are in cascaded form. This class of underactuated systems can represent many real applications after transformations. In the controller design, the sliding surface is designed to stabilize the indirectly controlled modes. Its insensitivity to the model errors, parametric uncertainties and other disturbances and its ability to globally stabilize the system are two advantages of the sliding mode controller. (C) 2007 Elsevier Ltd. All rights reserved.