[en] This study investigates the nature of the nitrate concentration and its effect on the quality of groundwater in the Bara basin in North Kordofan State Sudan. The principal objective of this study is to: detect possible NO₃ sources affecting groundwater quality. The δ₁₅N results included two range of values, which suggested two different nitrogen sources in different parts of the study area. The data used in this study includes lithological logs, pumping and recovery data and chemical analysis. Rock ware, surfer, aquitest and aquichem software programs were used to analyze the data. which is the based on the lithological logs from nine shallow wells and seven deep boreholes. The geological formation was found to be the Umm Ruwaba formation which consists of two aquifers an upper shallow one and the other deep aquifer. The transmissivity of the upper aquifer was found to be 0.528m² / day, which is good and the average of hydraulic conductivity was found to be 0.08₄ m/ day, which is high and the storativity is 0.08₁. The direction of flow of groundwater was found to be from North West to North East over all the area. Chemical analysis showed that the TDS concentration in the study area is within the permissible limits of the Sudanese and the WHO standards. The calcium concentration in the study area also found to be within the permissible limits of the Sudanese and the WHO standards. The nitrate concentration in the upper aquifer ranges between 9.68 and 891 mg/1 which is above the permissible limit of the Sudanese and the WHO standards. The water type in the upper aquifer was found to be calcium-nitrate-chloride-bicarbonate. It appears that the source of the calcium is either for the decay of dead animal bones or the dissolution of calcareous deposits within the upper aquifer. It can be concluded that the quality of groundwater in the study area is good for the human consumption. (Author)