Determination of naturally occurring gamma emitting radionuclides concentration are of a great importance for the assessment of external and internal radiation dose received by human. The level of natural radioactivity of 65 rocks samples collected from different locations at Kalrayan Hills, Tamilnadu, India, was measured. Activity concentration of radionuclides in samples were determined by γ-ray spectrometer using NaI(Tl) crystal detector with specially designed shield. The average radioactivity concentration of 238U, 232Th and 40K were determined and expressed in Bq/Kg. The result shows that these radionuclides were present in the range BDL to 22.90±5.81 Bqkg-1 for 238U, BDL to 91.60±6.43 Bqkg-1 for 232Th and BDL to 505.00±29.57 Bqkg-1 for 40K. Also, to know about the radiological hazard, the absorbed dose rate was calculated from the measured activity concentrations.
