The aim of study is designed of Power System Stabilizer (PSS) based on H_∞ approach for power system stabilization. The uncertainties in power system modeling and operations are considered at designing of H_∞ PSS. The bounds of power system parameters are determined over a wide range of low frequency operating conditions. These bounds are used to design a robust H_∞ PSS. A sample power system composed a synchronous generator connected to infinite bus through transmission line is simulated. The digital H_∞ PSS can achieve good performance over a wide range of operating conditions. A comparison between power system responses at variety of operating conditions using the proposed H_∞ PSS and Linear Quadratic Regulator LQR control have been done. H_2 PSS is designed and compared with the proposed controller.