Preparing aquifer vulnerability maps has become crucial during recent years for preventing adding new ones to aquifers which have been contaminated due to environmental effects and been out of use. GIS techniques and DRASTIC method were used when preparing vulnerability maps for the basin in which the Gumushacikoy and Merzifon aquifers are located. Groundwater flow is approximately directed west-east and many villages are located across the aquifer in the basin which contains two sub-provinces and is characterised by intensive agricultural activity. DRASTIC layers were created when preparing vulnerability map, using parameters such as groundwater level, recharge, aquifer environment, topography and hydraulic conductivity. The aquifer vulnerability map was prepared by overlapping the layers by means of GIS. , three different vulnerability zones were determined in the Gumushacikoy basin according to DRASTIC scores low (<100), medium (100-140) and high (>140). Based on the vulnerability map, it was found that the Gumushacikoy Basin had a low contamination potential. It was established that 16% of the basin had high vulnerability and 47% low vulnerability. Areas having high vulnerability generally overlapped areas where the slope was gentle soil above the aquifer was permeable.