Volume 10 Article informations Assessing vulnerability to agricultural pollution of groundwater Bou Arada-Laroussa according to SI method applied by GIS Sinda Gaieb,Mohamed Hafedh Hamza Abstract Groundwater of Laroussa Bou Arada is located in an agricultural area characterized by using increasingly important chemical fertilizers and especially nitrates. A study of vulnerability to nitrate pollution of the aquifer has been performed by applying the SI (Susceptibility Index) parametric method by Geographic Information Systems represented by the softwares Idrisi Andes and Cartalinx. The results were validated by measurements of nitrates in the groundwater. Three vulnerability classes (low, medium and high) were obtained showing an uneven spatial distribution. Much of the study area belongs to the class of medium vulnerability (70% of the total area), followed by the class of high vulnerability (29.86 %) and the low vulnerability class that covers only 0.14 % of the total area of the study area. The total coincidence rate between nitrate concentrations and different vulnerability classes is 71 %, which allows the validation of the vulnerability map obtained. This card can be used as a tool for decision support in planning and thus better protect the groundwater in the study area. Key words: Vulnerability, Groundwater, Pollution, Nitrates, SI method, GIS, Siliana-Tunisia.