Recently, desertification as a great problem threaten many countries all over the world. For evaluation and mapping of desertification many researches have been conducted in other countries leading to regional and local models. The present study attempts to assess quantitatively the desertification process to develope a regional model in Tabas masina region southe khorasan with area of about 25000 ha as a case study. In this study, based on the MEDALUS method and according to the characteristics of study area a regional model was developed using GIS. In the first step, all major factors affecting desertification were determined. These main eight indicators (layers) included: soil, climate, erosion, plant cover, groundwater, phisigraphy, Geology, and management (for human activities). Then a number of sub-layers for each main layer affecting the quality of main layers were identified. To each sub-layer a number between “1 to 2” according to the MEDALUS method was denoted. These denoted numbers were considered as a weight for each sub-layer. GIS (ArcGIS) then was used to analyze data to prepare the main layer status maps using geometric mean for the sub-layers and the main layers. Ultimately, the maps were combined and based on the geometric mean of the main layers, a desertification potential status map and sensitive map of the area was developed. The results indicated that 5/3% of total study area Keywords: Medalus model, Desertification, Southern Khorasan, Tabas-Mesina Vicinity
