I do not know what I may appear to the world, bu.t to myself I seem to have been only like a boy playing on the seashore, diverting myself in now and then finding a smoother pebble or a prettier shell than ordinary, while the great ocean of truth lay all u.ndiscovered before me.

This paper presents a design framework for the stabilization of a class of underactuated mechanical systems. By utilizing nonregular static state feedbacks, these systems are transformed into a class of nonlinear systems with chain structures. Then, controller design is presented by applying the backstepping design technique. The design procedure is applied to an underactuated robotic system and simulation tests are carried out for illustrating the effectiveness of the proposed approach.