In the present study, DRASTIC model has been used as a feasible methodology to assess the groundwater vulnerability in the Walawe river basin, Sri Lanka. The main objective of the study is to assess the potential level of groundwater vulnerability for pollution and to compare the areas with land use activities representing the degree of usage of fertilizers in agriculture. The Geographical Information Systems (GIS) has been used to develop vulnerability maps, showing the relative vulnerability of the area. The results concluded that the upper part of the basin shows very low vulnerability and the lower part shows higher vulnerability for groundwater pollution. The ground water vulnerability maps are compared with the agricultural land use pattern of the area and it is noticed that the areas with intense agricultural activities, overlapped with the areas with high DRASTIC index values. In the area with higher DRASTIC index and with intense agricultural activities including the extensive usage of fertilizers and pesticides, more attention should be focused to establish monitoring network for adequate groundwater quality control and to reduce the anthropogenic stress on groundwater resources.