Peroxidase (abbreviated as POX or MPO) is a type of oxidoreductase produced by microorganisms or plants that can catalyze many reactions. Peroxidase catalyzes the oxidation of substrates using hydrogen peroxide as electron acceptor, and mainly exists in the peroxisome of carriers. With iron porphyrin as cofactor, it catalyzes hydrogen peroxide, oxidation of phenolic and amine compounds, and has the dual effect of eliminating the toxicity of hydrogen peroxide and phenolics, amines, aldehydes, and benzenes.

Peroxidase Staining Solution (Oxidized WG-KI Method) can be used for peroxidase staining of blood, bone marrow, or cell smears. POX active sites appear as brownish-red to bluish-black particles localized in the cytoplasm.