The natural radioactivity existed since creation of the universe due to the long life time of some radionuclides. This natural radioactivity is caused by gamma-radiation originating fromthe uraniumand thoriumseries and K-40. In this study, the gamma radiation has been measured to determine natural radioactivity of U-238, Th-232, and K-40 in collected sedimentary rock samples in different places of Turkey. The measurements have been performed using gamma-ray spectrometer containing NaI(Tl) detector and multichannel analyser (MCA). Absorbed dose rate (D), annual effective dose (AED), radium equivalent activities (Ra-eq), external hazard index (H-ex), and internal hazard index (H-in) associated with the natural radionuclide were calculated to assess the radiation hazard of the natural radioactivity in the sedimentary rock samples. The average values of absorbed dose rate in air (D), annual effective dose (AED), radium equivalent activity (Raeq), external hazard index (H-ex), and internal hazard index (H-in) were calculated and these were 45.425 nGy/h, 0.056mSv/y, 99.014 Bq/kg, 0.267, and 0.361, respectively.