In this paper, a new PSO based PSS is proposed for the UPFC to damp power system low frequency oscillations. In order to damp the power systems oscillations effectively, Power system stabilizer is proposed for UPFC. The parameters of PSS are tunned using PSO algorithm. The effectiveness of the proposed control strategy is evaluated under different fault conditions in comparison with the GA based PSS to demonstrate its robust performance through time simulation studies and specific performance indices.