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Mass movelnent is one of the natural phenomena that causes considerable damage in different regions of Iran. Galeh Shour landslide in Chahar Mahale Bakhtiari is one of the problems caused by road to Khoozestan province construction. The dimensions of this landslide ara 125 m length,
110m width and 24m depth. The effective factors on landslide such as topography, weather, geology, tectonic, geomorphology, vegetation cover, physico - chemical and mechanical characteristics of sliding mass were determined and compared with regular hill slopes. Accordingly, uniformity of geologic formations with topographic slope (20-400/0), susceptibility of marl formations and their expanding when subjected to water absorption and because of dominant mineral of smectite, low plasticity, degradation of vegetation cover, annual precipitation in the form of rain and snow (680 Inm), and road construction on hillslope intensify the landslides. The stability analysis of the hillslope using stable software shows that landslide has occurred in depth of 24 m. The estimated volume of sliding mass was about 1 72,000 m3 . Based on plastic and liquid limit of the Inass (LLm=30.150/0 and PL=28.6%), about 52069-83932 m3 of water is needed for this landslide to occur. According to the annual precipitation and area (150 ha) of up hill in sliding mass, about 152603 m3 of \vater has entered the mass. With this absorbed water, the moisture of mass reaches plastic and liquid limit and even more. In addition to the mentioned effective factors on landslide, other factors such
as tectonic and road construction in down hill intensify the occurance of landslide in this rgion.