Determination of swelling in addition to clay mineralogical composition is important to clarify the contribution of clays on the occurence of landslide . The clay fractions (<2μm) separated from landslide areas of Okinawa (Shimajiri mudstone), where the contribution of clay was estimated to be relatively low, contained clay mica, smectite and chlorite as dominant clay minerals . The smectite content was relatively low with a value of about 30%, and its swelling was again low . On the other hand, the clay fraction separated from landslide area of Kamenose, Osaka, where the contribution of clay was estimated to relatively high, contained about 90% of smectite and its swelling was high.