The active suppression of vibrations of spacecraft flexible appendages during attitude tracking or large-angle maneuvers is discussed. On the basis of a model obtained using the Lagrangian approach and the unitary quaternion parameterization,piezoelectric actuators are used to damp the vibration of flexible booms induced during the maneuvers: The results of simulation reveal the interest and the practical feasibility of such a control scheme. The control law requires only the measure of the attitude and the angular velocity. The absence of flexible displacement and velocity sensors is compensated for by the presence of appropriate dynamics in the controller.