Thiosulfate is an excellent reducing agent. It is used primarily as an "antichlor" or chlorine-removing agent in various chemical processes, including the bleaching of pulp, paper and textiles. Other applications include the manufacture of leather and as a "fixer" in photography.

The Titrimetric Method. CHEMetrics' method employs iodide-iodate reagent. Although sulfite usually titrates as thiosulfate, the reagent has been formulated to inhibit high-level sulfite interferences. Thiosulfate is titrated with iodide-iodate titrant in acid solution using a starch indicator. Results are expressed as ppm (mg/L) S₂O₃.