The performance of a commercialized power system stabilizer (PWX-600) for a single hydro-turbine generator and infinite bus system has been investigated using Real Time Digital Simulator (RTDS) in this paper. The test system was composed of RTDS, three phase voltage/current amplifier and the PSS. The test scheme provided a very efficient way to verify the design and control performance of a PSS to be applied to real power system. The scheme can also be applied to verify in real time the performance of hardware and software of power system controllers for FACTS and protective relays effectively.