This research was conducted to recognize Sibak-Sardab watershed rangeland potentials, evaluate and determine of suitability classes for sheep grazing. In this research, we used the proposed method of FAO (1992) and for information layers crossing used in Geographical Information System (GIS). In this research, sensitivity to erosion, water resources and forage production are three basic components of this study. We used the MPSIAC model for the sensitivity to erosion. The model of water resource suitability consists of three parameters, quantity, quality and water resource's accessibility. In the forage production model, we estimated the ratio of available forage to the whole produced forage in each vegetation type. According to the result 96% of the rangeland was in low suitability class (S3) and only 4% were in medium suitability class (S2). The most important factors causing the decrease in suitability were lower rates of available forage for the livestock, low forage production of classes, I, II and low palatability percentage. According to Actual use (22170 animal units in season grazing); and grazing capacity (15989 animal units) and also according to the high destruction because of heavy grazing; using a management method that can help to improve the rangeland condition is suggestion.