Abstract: Ten fresh rock samples were collected from three rivers in Osun State, namely Erin-Ijesha (EI), Osun-Osogbo river (OS) and Ishasha river in Edunabon near Ile-Ife (IS). The study area is underlain by the Precambrian Basement Complex of southwestern Nigeria. This is to determine their radioactive heat production and the contribution of each radionuclide content. The radiogenic heat production was determined by spectrometer which gives the area photopeak of the radionuclides contribution. These photo peaks were later converted to Bq Kg-1 and part per million (ppm) for radiogenic heat computation. The result shows that concentration and rate of heat production of 40K, 238U and 232Th in the samples varies significantly with geological location. The total heat production ranges from 8.21 to 235.82 pW kg-1. The highest concentration and heat production is recorded in Quatz of Osun-Osogbo rivers and the heat produced by 40k is highest in six samples. It is also noted that rock samples from Erin-Ijesha river are associated with high heat production of 232U.