To clarify amplification characteristics of earthquake motion and own natural periods of landslide masses, we analyzed observed data of seismometer which installed at three different depths in the Yuzurihara and the Yui landslides. As a result of the analysis, maximum acceleration above the sliding surface showed 1.0 to 1.9 times larger than the basement layer. The maximum acceleration of the subsurface showed 1.1 to 3.6 times larger than the basement layer. In the Yuzurihara landslide, own natural periods of the landslide mass in horizontal and vertical are estimated to be about 0.22 to 0.25 seconds and 0.10 to 0.13 seconds, respectively. The own natural periods of the Yui landslide in horizontal and vertical are estimated at around 0.37 seconds and 0.20 to 0.22 seconds, respectively. In Yuzurihara landslide, the period indicating the maximum of the acceleration Fourier amplitude spectrum and the own natural periods showed different values. In Yui landslide, the period indicating the maximum of the acceleration Fourier amplitude spectrum of horizontal direction and the own natural periods showed same values. Since the landslide displacement had not been recorded in the Yui landslide, we estimate the monitored acceleration is smaller than the value which causes landslide displacement.