Abstract: It is very important to determine the thermal neutron flux spectrum at theirradiation sites of the MNSR. Five activation detectors ~(164)Dy, ~(151)Eu, ~(176)Lu, ~(151)In,~(197)Au are used in this work, and thermal neutron flux spectrum in the thermalcolumn of SPR reactor is used as a reference spectrum. The ratio of the detectedactivities in MNSR and the detected activities in SPR are determined, the developedspectrum in MNSR is obtained. The parameters of the spectrum are calculated andcompared with experimental data. The results are satisfactory.