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The paper deals with the study of natural radioactivity in the rocks of Coorg district, Karnataka state. The samples were analyzed by NaI(Tl) based gamma ray spectrometer. The activity of Th-232 varies from 16.46 Bq kg(-1) to 160.84 Bq kg(-1) with mean value of 79.05 Bq kg(-1). The activity of K-40 varies from 96.72 Bq kg(-1) to 933.68 Bq kg(-1) and that of Ra-226 was found to vary from BDL to 34.36 Bq kg(-1). A correlation coefficient of R = 0.81 was found between Th-232 activity and K-40 activity. The correlation between Ra-226 activity and Th-232 activity is R = 0.59. The correlation between K-40 and Ra-226 is R = 0.51. The Radium Equivalent Activity (Raeq) ranges from 46.78Bq kg(-1) to 315.55Bq kg(-1). The absorbed gamma dose rate (D) ranges from 21.28 nGy h(-1) to 141.45 nGy h(-1), with an average of 73.37 nGy h(-1). The radionuclides activity was compared with world average values. The external Hazard index (Hex) varies from 0.12 to 0.84. The internal hazard index (Hin) is in the range 0.15-0.89. The hazard indices were found to be within safety limits. (C) 2017 The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B. V.