Nowadays, the continuous growth in power demand leads to expansion of the Power System network which makes existing system more sensitive and prone to instability. An important issue associated with the stability of a multi-area power system is low-frequency electromechanical oscillations from the multi-machine system. Generally, Power System Stabilizer (PSS) are used to compensate low-frequency electromechanical oscillation of interconnected Power System, but local PSS does not have global observance and controllability of inter-area low-frequency oscillation because of a control signal of local PSS and generated a local signal. So next resolution is Flexible AC Transmission System (FACTS) device with supplementary controller, that are used for effective damping of low-frequency electromechanical oscillations of interconnected Power System and to improve Power System stability. This paper presents Coordination control of PSS and FACTS Devices to damp out low-frequency electromechanical oscillation. In this research study, we use different FACTS Devices like Static VAR Compensator (SVC), Static Synchronous Series Compensator (SSSC), Static Synchronous Compensator (STATCOM), and Unified Power Flow Compensator (UPFC) to damp out low frequency electromechanical oscillation from a Multi-machine Power System and improve the stability of Interconnected Power System. Analyzing result of all FACTS devices on simulation, we found that UPFC gives a better response. Due to re-activeness, FACTS device like UPFC are considered and assessed for their damping controller design. In this research, we studied the implementation of supplementary Power Oscillation Damping (POD) Controller to control UPFC. POD Controller are designed to improve the dynamic performance of interconnected Power System under the transient condition to stabilize Power System. Some simulation results are carried out on Kundur Two area Four Machine systems under small disturbances. From simulation result, it reveals that the proposed controller damp-out low-frequency electromechanical oscillations effectively to improve Power System stability under small disturbance.