One of the best ways, to prevent groundwater resources from contamination, is identifying the aquifer vulnerability areas, and monitoring groundwater quality spatial variations to manage the groundwater exploitation and the land usage. In this research, for the first time, the aquifer vulnerability map of Gachsaran Emamzadeh Jaafar, located in South of Kohgiloyeh and Boyrahmad province, is evaluated using DRASTIC model. Investigating of hydro geological parameters impact on aquifer vulnerability, and the results of sensitivity analysis, using both the map removal and single parameter methods, indicate that the zone (I) has the most significant impact on the vulnerability index. Based on the DRASTIC results, about 4.2, 56.2 and 37.0 % of Emamzadeh Jaafar aquifer have high, moderate, and low vulnerability, respectively, and the vulnerability of 2.6% of the areas is negligible. Since the high vulnerability areas is covered upstream of the aquifer, entrance of any contaminants can be distributed in groundwater flow direction.In addition, the potable groundwater variations map, prepared based on GWQI index, and the result from its comparing with the Schaller diagram, shows that 1.6, 83.4 and 12.1 percentages of groundwater resources in Emamzadeh Jaafar aquifer have excellent, good and bad quality. In general, the groundwater quality of most area is good, except in North West part of the aquifer, which has poor groundwater quality due to flowing through the evaporated Gachsaran formation.