The peroxydisulfate ion, S2O2−8, is an oxyanion, the anion of peroxydisulfuric acid.

These salts are colourless, water-soluble solids that are strong oxidants.

[3] Salts of peroxydisulfate are mainly used to initiate the polymerization of various alkenes, including styrene, acrylonitrile, and fluoroalkenes.

Polymerization is initiated by the homolysis of the peroxydisulfate: Moreover, sodium peroxydisulfate can be used for soil and groundwater remediation, water and wastewater treatment, and etching of copper on circuit boards.

[4][2] It has also been used to produce hair lighteners and bleaches, medical drugs, cellophane, rubber, soaps, detergents, adhesive papers, dyes for textiles, and in photography.