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Western Japan 60 Hz power system is a longitudinal power system which consists of interconnected six major electric power companies. Though the power system has some interesting oscillation characteristics, there were few researches based on observation as a whole system. Authors have constructed an online global monitoring system of the power system dynamics, which is based on multiple synchronized phasor measurement technique using time stamp of the Global Positioning System (GPS) and Internet. This paper presents some results of observing system frequency oscillation and discussed the difference among the measured point. System dynamics due to the load frequency control (LFC) can be extracted from observed frequency oscillations by time-frequency analysis based on the Wavelet transform. Because variations of phase difference between the interconnected two areas are closely related with tie line power flow variations, relations between the frequency oscillations and the LFC are also investigated.