Power System Stabilizers (PSSs) are used to enhance damping of power system oscillations through excitation control of synchronous generator. The objective of the PSS is to generate a stabilizing signal, which produces a damping torque component on the generator shaft. Conventional PSSs are designed with the phase compensation technique in the frequency domain and include the lead-lag blocks whose parameters are determined according to a linearized power system model. The performance of Conventional PSSs (CPSSs) depends upon the generator operating point and the system parameters, but a reasonable level of robustness can be achieved depending on the tuning method. To overcome the drawbacks of CPSS, numerous techniques have been proposed in literatures. In this paper a robust method based on Quantitative Feedback Theory (QFT) Algorithm is used for tuning the PSS parameters. The proposed QFT-PSS is evaluated at a multi machine electric power system. The simulation results clearly indicate the effectiveness and validity of the proposed method.