Abstarct: The aim of this study is a robust controller design of Static Synchronous Compensator (STATCOM) to achieve an optimal stability against power system oscillation. The design of proposed controller is baxsed on μ-synthesis. Generally, D-K method is used to solve μ-synthesis. The weakness of this method is that it leads to a high-order controller. The proposed design method in this thesis is presented to cope with this weakness, baxsed on an optimization problem and Teaching-Learning-baxsed Optimization (TLBO) algorithm is used to reduce controller's order. Finally, the stability and performance of the proposed controller is compared with other conventional controllers, and in the simulation results, the superiority of the proposed controller is observed.