Background: The present work aims to determine the activity concentrations of 226Ra, 233Th and 40K in soil samples collected in Mounana in the Southeastern region of Gabon, to evaluate the contribution of the natural. Materials and Methods: An HPGe p-type detector coupled with a multichannel analyzer DSA-1000 was used to perform measurements and process data. Data acquisition and analysis were made possible  using Genie 2000 software version 2.1 and detector was calibrated using the IAEA certified soil reference standard material multi-gamma (No71863/3). Results: The activity concentrations of ²²⁶Ra,²³²Th and ⁴⁰K varied respectively from 12 ± 03 Bq kg^-1 to 23022 ± 2572 Bq kg^-1, 12 ± 04 Bq kg^-1 to 265 ± Bq kg^-1 and64 ± 13 Bq kg^-1 to 811 ± 74 Bq kg^-1with means values of 2811 ± 198Bq kg^-1, 63 ± 14 Bq kg^-1 and of 355 ± 93 Bq kg^-1wet weight. In order to assess the radiological risks due to primordial radionuclides in Mounana, the absorbed dose rate, effective dose, radium equivalent and external hazard index were estimated. Conclusion: Absorbed dose rates which have been calculated for each site varied from 26.12 nGy h^-1 to 10817.99nGy h^-1 with a mean value of 1352.76 nGy h^-1. The mean value of annual effective dose was estimated to be 10.96 mSv y^-1 from the studied area. The areas investigated in this study showed a strong radioactive contamination of sites inhabited by populations.