Northern Thailand is prone to landslides. The test site is Cheangklang district in the middle of drainage basin of the Nan River, Nan Province. The study area is about 297 km2 , with 75% of mountain area and mean elevation range in 600 - 1000 m. above mean sea level. Conventional investigation methods, relationships between landslide factors and environmental factors have been preliminary assessed through statistical analysis. All the data from the principal databases have been integrated within a GIS environment, in order to produce the preliminary map of landslide disaster. This procedure has been coupled with an intense geological interpretation phase, characterized by the analysis of traditional in situ monitoring data, ancillary data, field surveys, sampling and laboratory tests. The weight factors indexes interpretation, have been improved by the use of slope stability analysis techniques, using the factor of safety. Shear strength and hydraulic conductivity property of soil slope were tested. The factor of safety values were input into GIS and landslide disaster risk area rating were assessed for each class of the final map.