Abstract: Soil samples collected around a nuclear installation in southwest China have been analyzed for U, Th and K using instrumental neutron activation analysis (INAA). Samples were irradiated with an integral thermal neutron flux of 3×10¹⁷/cm² in the high flux reactor at Nuclear Power Institute of China, Chengdu, China. The three elements have been determined from 150 samples by high-resolution gamma spectrometry. To evaluate the accuracy of analytical data, certified reference materials NIST SRM 1633a and GBW 07045 were analyzed together with unknown samples and the results were found to be in good agreement with certified values for these three elements. The results of correlation analysis for both the contents of the three elements and the Th/U ratio indicate that the nuclear field releases a little uranium to environment. Moreover, the results of size distribution indicate that the uranium and thorium contents are higher in clay than in other kinds of soil particles, especially for uranium.