Power Swing Blocker (PSB) is a complementary part in distance relay that detects power swing in the transmission line to prevent unintended operation of distance relay. Unified Power Flow Controller (UPFC) is used in a transmission line to control active and reactive power. The UPFC operation during power swing influences the performance of PSBs in different ways. In this paper, two methods (the center of circular impedance trajectory and the rate of change of power) for detecting power swing are analyzed in UPFC-compensated condition to show how UPFC influences the performances of these methods. The proposed indices of these methods are examined in compensated condition and it is shown that these indices may no longer work.