Nitrate pollution of groundwater is an increasingly serious anthropogenic problem. In this study, the hydrogeochemistry of major ions and stable isotope ratios of NO3- in groundwater were determined to identify the contamination sources and chemical transformation processes occurring in the shallow groundwater of Xi’an, the capital of Shaanxi province, NW China. Of a total of 32 groundwater samples, 31% had NO3-–N concentrations exceeding the accepted drinking water limit of 10mg-NL −1 . Most of these samples were from the urban center of the study area, while samples with <10mg-NL −1 were mainly from suburban areas. Combined with information on NO3- and Cl − , the variation in isotopes of NO3- in the groundwater suggest a mixing of multiple NO3- sources in areas on the urban/suburban border. By determining rainwater and river water NO3- isotopic values, the groundwater recharge mode can be deduced for Xi’an city. Chemical fertilizers and nitrification of N-containing organic materials contribute NO3- to suburban groundwater, while sewage effluent and nitrification dominate NO3- distribution in urban groundwater. Nitrification from organic soil N, manure and sewage was significant in some sampling areas, and NO3- isotopic values from groundwater in Xi’an indicated that the effects of denitrification were not an obvious contributor. Thus, the δ15N–NO3- enrichment process is mainly caused by the intense anthropogenic activity in the city center. From the urban center to suburban areas, the mean δ15N–NO3- values varied from +16.4‰ to +5.4‰, and the mean NO3-–N concentrations varied from 28.0mgL −1 to 4.0mgL −1 . In particular, the δ15N–NO3- value (r=−0.75, p<0.01) correlated more significantly with distance from the urban center than did the NO3-–N concentration data (r=−0.49, p<0.01), which suggests that NO3- isotopic values are an effective indicator of contamination sources. In addition, the δ15N–NO3- values and population density show a significant logarithmic correlation in Xi’an city.