PURPOSE: To obtain hydroxylamine nitrate efficiently, in producing hydroxylamine nitrate from hydroxylamine sulfate and nitric acid by electrodialytic method by using only a cation exchange membrane as an ion exchange membrane.

CONSTITUTION: An electrodialytic tank 2 is partitioned by a great number of cation exchange membranes 1 into a large number of chambers, an aqueous solution 5 of hydroxylamine sulfate is circulated through every other chamber, an solution 6 of nitric acid is circulated through the residual every other chamber and DC voltage is impressed from an electrical source 9 between an anode 3 and a cathode 4. Consequently, hydroxylamine of hydroxylamine sulfate is drawn to the anode 3, permeated through the ion exchange membranes 1 and transferred to the side of the aqueous solution of nitric acid. Hydrogen ion in then aqueous solution of nitric acid is transferred t neighboring chambers, the remaining nitrate ion is bonded to the permeated hydroxylamine ion to form hydroxylamine nitrate. The nitrate is useful as a reducing agent for re- treating process of used nuclear fuel.