In this study, the nonlinear aeroelastic characteristics of a wing with an oscillating control surface have been examined in transonic and supersonic regimes. The various effects of rotational stiffness on flutter have also been observed. A modified transonic small-disturbance (TSD) theory is used to more effectively analyze the unsteady aerodynamics of a wing with an oscillating control surface. In the flutter analysis, a coupled time integration method (CTIM) and a transient pulse method (TPM) were used to examine the effects of rotational stiffness reduction on the control surface. The present study shows that the severe decrease of flutter speed and the flutter mode transition can be induced by the reduction of rotational stiffness. In particular, it is shown that the aerodynamic effects of control surface oscillation play an important role in this flutter speed reduction. (C) 2004 Elsevier SAS. All rights reserved.