In the last two decades, industrial and research applications which needed to high-precision positioning have grown rapidly and widely. Piezoelectric actuator is one of the most useful choices in this field. Despite the high resolution, linear and nonlinear dynamics of this actuator, such as hysteresis, could decrease the closed-loop control system performance. Hence, very diverse research has been done about the modeling and control of it. The purpose of this study is hysteresis compensation and precise position control of this actuator. The Bouc-Wen model and sliding mode control method are used for this goal. Most of the similar studies consider the hysteresis as an uncertainty or disturbance. This leads to a conservative controller and decrease in control system performance. The main innovation of this study is hysteresis compensation using its momentary value and closed-loop system stability analysis. The hysteresis is an internal state of system, and is not measurable. In this thesis, for hysteresis observation the high-gain observer is proposed and designed, firstly. Also, the observer-based controller and joint stability analysis are presented. For situation where the mass, stiffness and damping coefficient of the model are unknown, the control rule using the parameter adaptation is presented and its effectiveness is shown. For robustness against the unstructured uncertainty, sliding mode observer and controller are proposed and stability is proven. The sign function in sliding mode control could lead to chattering in actuator output and control signal. This phenomenon reduces the response quality and might result in failure of mechanical parts. Whereas using the functions such as saturation could reduce this problem, but it does not fundamentlly resolve it. Chattering is completely eliminated by the presented method. One of the problems of sliding mode control is the large control gain due to stability requirements, which leads to performance loss. For preventing this problem, the gain is adaptively estimated proportional to the closedloop system error. In summary, hysteresis compensation using its momentary value, joint stability analysis of observerbased controller, robustness against the structured and unstructured uncertainty, chattering elimination and adaptation of the controller gain are the advantages of the presented methods. The proposed methods are validated using simulation and experimental results. The experimental tests are done using the real actuator, laboratory setup and LabVIEW software. Also, the results are compared to other methods using quantitative criteria. Key Words : 1- Piezoelectric actuator, 2- Hysteresis phenomenon, 3- Observer-based controller, 4- Joint stability proof, 5- Chattering, 6- Sliding mode control