The aim of this study is to investigate the efficiency of a system identification technique known as observer/Kalman filter identification (OKID) technique in the numerical simulation and experimental study of active vibration control of piezoelectric smart structures. Based on the structure responses determined by finite element method, an explicit state space model of the equivalent linear system is developed by employing OKID approach. The linear quadratic Gaussian (LQG) algorithm is employed for controller design. The control law is then incorporated into the ANSYS finite element model to perform closed loop simulations. Therefore, the control law performance can be evaluated in the context of a finite element environment. Furthermore, a complete active vibration control system comprising the cantilever plate, the piezoelectric actuators, the accelerometers and the digital signal processor (DSP) board is set up to conduct the experimental investigation. A state space model characterizing the dynamics of the physical system is developed from experimental results using OKID approach for the purpose of control law design. The controller is then implemented by using a floating point TMS320VC33 DSP. Numerical examples by employing the proposed numerical simulation method, together with the experimental results obtained by using the active vibration control system, have demonstrated the validity and efficiency of OKID method in application of active vibration control of piezoelectric smart structures.