Abstract: The miniature neutron source reactor (MNSR) is based on highly enriched uranium (²³⁵U) as fuel and light water as moderator. Because of a larger share of epithermal neutron and fast neutron in irradiation channel, the reactor is suitable for epithermal neutron activation analysis (ENAA). In general neutron activation analysis the main component elements in complex geological samples such as aluminum, sodium, iron and so on affect the determination accuracy of some target elements. In order to reduce the interference of the background of main component elements and improve the precision and detection limit of the target element, the ENAA can be used in the test of geological samples. By using epithermal neutron irradiation channel made of cadmium, the Cd ratios of about 130 nuclides of 67 elements in the periodic table were measured. The advantage factors of some elements and the interferences of uranium fission and (n, p) reaction in ENAA were discussed. The practical application of MNSR ENAA method in testing of geological sample was verified. The results show that more than 20 kinds of elements can be ascertained in the sample measuring by this method. The detection limit, precision and accuracy are more significantly improved. The MNSR ENAA is a necessary and beneficial supplement of the conventional activation analysis method.