Abstract: This study was carried out to assess the desertification severity and sensitivity in the Northern part of the Gorgan plain, Southeast of the Caspian Sea. Desertification is a global environmental hazard, but it is the most urgent ecological problem in the Gorgan plain, Iran, Southeast of the Caspian Sea. Success in combating desertification requires assessment and mapping of desertification sensitivity in arid and semi arid environment. Considering the environmental condition of the study area, in the current research the regional model of MEDALUS has been modified. The key indicators for defining environmentally sensitive areas in the original MEDALUS model area divided into four broad categories including soil, climate, vegetation and management quality indices. In this research two other categories of erosion and waterlogging indicators have been incorporated into the modified MEDALUS model. For each key indicator several sub-indicators affecting their index quality were identified. Based on the MEDALUS approach, each sub-indicator was quantified and a weight between 1.0 and 2.0 was given. Using ArcGIS 9, layers or maps of subindicators’s weight for each main indicator have been prepared and their geometric mean has been calculated as the quality index of the main indicator. In turn the geometric mean of all six quality indices was used to generate a desertification severity index map. Results showed that 52.94, 44.27 and 2.79% of the area is severely, moderately and slightly affected by desertification, respectively. In addition the soil and waterlogging indicators were the most important factors affecting desertification process in the study area.