The chemical composition of groundwater is affected by many features, including the impact caused by surrounding rocks. The Nile aquifer is surrounded by the calcareous structural plateau along Assiut governorate on both sides. This paper aims to study the effect of surrounding rocks on the chemical composition of groundwater in the Nile aquifer along Assiut governorate. Fifty five samples were taken from drinking water stations and irrigation wells in 2015, and then analyzed chemically in water and soil fertility laboratory in irrigation ministry in Assiut. Aquachem software package has been used to determine groundwater type and rock source deduction. Piper-trilinear diagram has been plotted to show the hydrochemical facies. Furthermore, Gibbs diagram has been applied to determine the correlation between water composition and aquifer lithological characteristics. The results revealed that nearly all of the groundwater samples drop in the water–rock interaction field. The results of rock source deduction show that the ratio of Cl to the sum of anions is less than 0.8 for all samples, concluding that the rock weathering is dominant. According to the criterion of TDS values, 78% of all the samples emphasized that the carbonate weathering is governed; whereas, the ratio of Mg to Ca plus Mg shows that limestone-dolomite weathering is predominant. This result confirms that the calcareous structural plateau surrounding the Nile aquifer along Assiut governorate has an effect on the groundwater chemistry by interaction between groundwater and limestone rocks which are the main component of the calcareous plateau.