PURPOSE: To provide a purification process which can give EDS-Na of high purity without repeated recrystallization by making the purification process a high-yield circulation method and limiting the waste products only to environmentally nonpolluting inorganic salts.

CONSTITUTION: In the purification process, the aqueous solution of sodium 1,2-ethanedisulfonate (EDS-Na) contaminated with inorganic salt impurities such as sodium halides, sodium sulfite or sodium sultate which is formed by oxidation of sodium sulfite is concentrated under atmospheric or reduced pressure until the solution is supersaturated to deposit almost all or a part of the inorganic salts. Then, the crystallized inorganic salts are filtered off while keeping the temperature of the slurry so as not to deposit the crystals of EDS-Na, and the filtrate is cooled down almost to the room temperature to crystallized EDS-Na, thus the purified EDS-Na is isolated by filtration at the ambient temperature.