Due to the increasing size and complexity of electric power systems, and also owing to the high rate of growth of electric power demand, electric power systems are often operated in a lower stability margin, therefore, real time stability monitoring is becoming more important for the reliable power system operation. In this project, a FFT based real time stability monitoring has been proposed for the modal analysis of power system oscillations in the frequency domain. The proposed real time monitoring system is set up by using a personal computer with a DSP board, which has an AD conversion interface for the measurements of real power flows to identify oscillation modes. The real power signal is recorded in the memory on the DSP board through the AD conversion interface and a sequence of stored real power signal is utilized for the FFT analysis in real time on the DSP board.. The result of FFT analysis is passed to the workspace in the Matlab/Simulink environment for the visualization of the oscillation modes using color mapping to show the variation in real time. In addition, a fuzzy reasoning based decomposition of individual oscillation modes has been performed to extract individual modes included in the measured real power flows. To have better understanding of power system oscillations in the study system covering a wide area, a coherency analysis has been performed. All the programs have been developed in the Matlab/Simulink environment for the entire process of the real time modal analysis. The proposed system has been tested by using power flow signals on 500kV trunk lines measured at 500kV substations in the Kyushu Electric Power System.