Over the past decades, the issue of low frequency oscillations has been of major concern to power system engineers.These oscillations range from 0.1 to 3Hz and tend to be poorly damped especially in systems equipped with high gain fast acting AVRs and highly interconnected networks.If these oscillations are not adequately damped, they may sustain and grow, which may lead to system separation and loss of power transfer.As a means to alleviate such problems of low damping in power systems, Power System Stabilizer (PSS) has been proposed.PSS produces a component of the electrical torque in phase with the rotor speed deviations, thus adding damping to the generators rotor oscillation.Results obtained in this work could be improved by carefully tuning the PSSs by including small and large disturbances conditions, within the objective function. It was found that a high gain value of the PSS slightly negatively affected the initial oscillations after the fault application. The initial oscillations have higher amplitudes due to the high gains. It is also suggested that the optimal locations of the PSS be considered within the optimization, especially for a Multi-machine syste