The present paper treats experimental investigation for optimal vibration control of composite plates with a bonded piezo film sensor and a piezo ceramic actuator. The plant parameters(A, B. C), and the Kalman filter gain(Kf) are obtained experimentally using ARMAX with modal truncation method. Based on these parameters, linear quadratic Gaussian(LQG) controller is applied to rectangular and wing-shaped composite plates using DSP board. Butterworth filter is used to prevent spillover phenomenon, and to smoothen the control signal. The experiments show that the vibration levels of three modes are reduced significantly.