Major ions and nitrogen isotopic analyses were performed to determine the geochemical characters and to identify the source of nitrate of the shallow groundwater around agricultural field in the Youngdong area. The pH value of groundwater ranges from 60. to 8.2 (pH 7.2, mean). The average of EC, Eh and DO is 369 µS/cm (70~729 µS/cm), 165.6 mV (29~383.2 mV), 4.3 mg/L (1.8~8.0 mg/L) respectively. The ion concentraion of groundwater was in the order of CaMost of groundwater is Ca-HCO 3 type. The groundwater was affected by water-rock interaction in the shallow depth. Some groundwater is Ca-Cl or Na-HCO 3 (2.5%) type that was due to agricultural activities. The NO 3 _N concetration of grondwater range from 10.2 mg/l to 26.9 mg/l, which show that this area is under nitrate pollution. δ