Five samples of sediments collected from southwestern Sinai - Egypt, have been investigated. The activity concentrations of radionuclides in sediment samples were determined by γ-ray spectrometer using HPGe detector with a specially designed shield. The values of activity concentrations of uranium are high in all sediment samples, and the activity concentrations of thorium are high in all samples except one sample, where the activity concentrations of 40K are low in most samples. The activity ratios between 226Ra/ 238U for sediment were calculated. Thorium to Uranium concentration ratios (Clark value) was also estimated. The uranium isotopes 234U, 235U and 238U are found naturally in the environment. 235U and 238U are present nuclides of two independent decay series of isotopes, while 234U is member of the 238U decay series. When decay series occur in closed system the series tends to reach, with time, the state of secular equilibrium in which the activities of all series member are equal to the activity of its first nuclide. The 234U/ 238U activity ratio obtained indicated that these two uranium isotopes are in the state of secular radioactive equilibrium.
