Mechanical characteristics and movement mechanism of landslides in the area Owakudani-Sounzan area have been analyzed by various methods, such as measurements with tiltmeters and extensometers, observations of ground water levels and tests of soil mechanics, etc. From these, the following conclusions have been obtained.1) On the slope, of which the materials are composed of greatly altered rocks and clay, small landslides are sometimes detected, but large ones scarcely.2) Small landslides are characterized by slope failure, and their movements are influenced by precipitation.3) Small landslides often occur unexpectedly, and it is difficult to foreknow them.