The objective of this paper is to derive a new adaptive control law for the control of the rotation angle of a smart projectile fin using a piezoelectric actuator. The smart projectile fin consists of a flexible cantilever beam with a piezoelectric active layer, which is mounted inside a hollow rigid fin and is hinged at the tip of the rigid fin. The rotation angle of the fin can be controlled by deforming the flexible beam. In the closed-loop system, asymptotic trajectory tracking of the fin angle is accomplished. Simulation results are presented which show that trajectory control of the fin angle is accomplished in spite of large uncertainties using adaptive control law and the flexible modes remain bounded during maneuvers.