Groundwater is one of the most valuable natural resources and for that reason, itsprotection and management is vital for human evolution, socio-economic developmentand ecological diversity. Increasing human activities has caused more and moregroundwater environmental problems. Because of the known health and economicimpacts associated with groundwater contamination and the fact that this hiddenresource is not amenable to direct observation, steps to assess groundwatervulnerability must be taken. This study aimed to assess the groundwater pollution potentials of the north-eastern part of block XIX, Tamtsag basin, Mongolia as well as utilizing sensitivityanalysis to evaluate the relative importance of the model parameters. Based on thepremise that the soil-rock-groundwater system may provide a degree of protectionagainst contamination of groundwater by `self-purification or `natural attenuationdepending on its hydrogeological features; the normal DRASTIC methodology wasadopted in this study as a screening tool to ascertain whether an area is more or lessvulnerable to groundwater pollution. DRASTIC model, combines spatial datasets onDepth to groundwater, Recharge by rainfall, Aquifer type, Soil properties, Topography,Impact of the vadose zone and the hydraulic Conductivity of the aquifer to characterizethe hydrogeological setting and evaluate aquifer vulnerability. These seven parameterswere calculated from geological data, soil and elevation maps, andgroundwater level data of the study area. ArcInfo/G1S was used to demarcatevulnerable zones based on their vulnerability index. The aquifer vulnerability mapindicated that only a slight 2％ of the study area is under moderate vulnerability tocontamination. The remaining zone was determined to be in a low risk category. GIS greatly facilitated the implementation of the sensitivity analysis applied on theDRASTIC vulnerability index which otherwise could have been impractical. Thesingle-parameter sensitivity analysis has shown that aquifer media, soil media andtopography are the most significant environmental factors which dictate the highvulnerability of the study area. This highlights the importance of obtaining accurate,detailed, and representative information about these factors. The map removalsensitivity analysis indicated that the vulnerability index is highly sensitive to theremoval of aquifer media, hydraulic conductivity and the impact of vadose zone layersbut is least sensitive to the removal of the topography layer. The analysis has alsodemonstrated that all the seven parameters used to compute the DRASTIC model areall essentials in determining the vulnerability index. The present vulnerability maps should be regarded as an important tool inprioritization of areas for monitoring purposes.