[en] The radionuclide activities of ²³⁸U, ²³²Th, ⁴⁰K and ¹³⁷Cs were measured using high resolution gamma spectrometry system. The total organic matter (TOM) and carbonate contents were also measured in the surface sediments of three valleys downstream at the southern Egyptian Red Sea coast. These localities are characterized by the presence of mangrove swamps with dense aerobic roots that provide calm conditions for particulate and fine sediments settlement. ²³⁸U and ²³²Th recorded almost equal activity values in the studied localities and their occurrence in the localities indicated that the metal accumulation are due to the complex and multiple processes that characterize the mangrove environments including accumulation in particulate form with the fine sediments, absorption on iron and manganese oxides and hydroxides from the sea water, incorporation inside the carbonate frameworks and as detrital phase. ⁴⁰K showed obvious radioactivity in the three localities indicating the presence of terrestrial radionuclide. ¹³⁷Cs concentrations were not evident in the studied localities which may indicate non-significant artificial source of radionuclide activity.