Activity concentrations of 226Ra, 232Th and 40K of limestone samples collected from Kitui South have been measured using Hyper Pure Germanium (HPGe) detector gamma ray spectrometry. A total of 48 samples were collected from the limestone rock outcrops in the region. The average activity concentrations varied from 28.3 to 47.4 with a mean value of 35.9 Bq/kg and 87.4 to 142.6 with an average of 108.5 Bq/Kg for 226Ra and 40K respectively. 232Th was below detection limits in all the samples. The value of the absorbed dose rates, annual effective dose rates, external hazard index, gamma activity index and alpha index were all below the maximum recommended values for radiological safety and showed good comparison within other studies in the world.