[en] A radiochemical neutron activation analysis to determine tellurium in sodium hydroxide solution has been developed. Coprecipitation with Fe(OH)₃ was applied to preconcentration of tellurium. After the irradiation the tellurium is separated by solvent extraction with 4-methyl-pentan-2-one (MIBK) and determined using ¹³¹Te isotope. The purification of iron carrier to be used for the coprecipitation and the separation efficiencies of principal elements in the chemical process of this method were studied. The result indicates that the method has a high sensitivity for the tellurium, and the detection limit is 0.04 ppb. The method is applicable to the non-radioactive tracer testing to measure the transfer of radiotellurium, a fission product, in the sodium coolant of the fast neutron reactor. (author)