Directional movement of liquid droplets is of significance not only for certain physiological processes in nature but also for design of some microfluidic devices. In this study, we report a novel way to drive directional movement of liquid droplets on a microbeam with a varying or gradient stiffness. We use the energy method to theoretically analyze the interaction between a droplet and the elastic microbeam. The system tends to have the minimum potential energy when the droplet moves to the softer end of the beam. Therefore, a gradient change of the bending stiffness may be utilized to help the directional motion of droplets. Similarly, one can also drive droplets to move in a designed direction by varying the cross sectional geometry of the beam. Finally, some possible applications of this self-propelling mechanism are suggested. (C) 2008 Elsevier Inc. All rights reserved.