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Radionuclides have been recognized as a limiting factor of groundwater quality in the Middle East and Northeastern Africa. High levels of naturally occurring radioactivity, mostly from radium and radon isotopes, have been reported in waters from the Nubian Sandstone Aquifer System (NSAS) in several countries in the Middle East including the Sinai Peninsula of Egypt. This study aims at extending the existing data coverage by investigating radionuclide concentrations and their potential geological and hydrogeochemical controls in groundwater of the NSAS and the overlying alluvial aquifers in the Eastern Desert of Egypt. Radium isotope activities (Ra-226 and Ra-228) and uranium concentrations were analyzed in 39 groundwater samples from these aquifers. The shallow Nubian aquifer has Ra-226 and Ra-228 activities ranging from 0.016 to 0.750 and 0.018-1.421 Bq/L, respectively. The deep Nubian aquifer has Ra-226 and Ra-228 activities ranging from 0.019 to 0.051 and 0.014-0.248 Bq/L, respectively. The shallow alluvial aquifers have Ra-226 and Ra-228 activities ranging from 0.008 to 0.086 and 0.006-0.081 Bq/L, respectively. Groundwater in the Nubian aquifer may have Ra activities substantially in excess of the drinking water MCL values of the US Environmental Protection Agency (EPA), the European Union (EU), and the World Health Organization (WHO). The concentration of U varies from 0.06 to 33.06 mu g/L, 0.06-15.46 mu g/L, and 0.01-13.19 mu g/L for the shallow Nubian aquifer, the deep Nubian aquifer, and the shallow alluvial aquifers, respectively. U concentrations exceed the EPA and WHO MCL values in some wells, mostly from the shallow Nubian aquifer.