Abstract: The study area is located in the southwest part of Bisetoon Mountain, south of Kermanshah City in western Iran. Slide is the most common natural phenomenon in the area, which usually is triggered by heavy rainfall and seismic activities. Although there are few active slides in the area, but they are serious threats to population the infrastructures. The aim of this study is to indicate the main factors influencing the slope instabilities. The weights -of- evidence have been applied to evaluate the slide susceptibility using GIS. The relations between slide distributions with the physical parameters such as lithology, elevation, slope gradient, lineaments and distance from streams, vegetation and land use were analyzed by Bayesian statistical model. The weights of evidence were applied to calculate each factor’s weight for the Merek region in west Iran, with numerous slides. Factors (data layers) used for the preparation of the slide susceptibility map were obtained from different sources such as topographic maps, geological maps and satellite images. The results of the analysis of mapping were validated using previous and recent slide location. We found that six parameters namely, distance from stream, slope, land use, profile curvature, plan curvature and lithology show better correlation with slide susceptibility. In the study area of the present work, the methodology was tested by the means of consistent slides found in hillslopes of Nesar Kooh valley. Since most of the information related to slides susceptibility map is geo-spatial, GIS is capable to store, update, display, process, analyze and integrate the different geo-spatial data. Based on this study, six appropriate factors were selected for slides potential hazard mapping in the Merek area. Results of six selected factors are in a good accordance with recently occurred slides.