Peroxiredoxin (Prx) is in the peroxidase family, whose mammalian members have been known to contribute to cell proliferation, differentiation and apoptosis. Many isoforms (about 50 proteins), collected in accordance with amino acid sequence homology, particularly the amino terminal region containing active site cysteine residue, and the thiol specific antioxidant activity, distribute throughout all the kingdoms. Mammalian Prx consists of 6 different members grouped into typical 2 Cys, atypical 2 Cys Prx, and 1 Cys Prx. Except PrxVI belonging to the 1 Cys Prx subgroup, the other five 2 Cys Prx isotypes have the thioredoxin dependent peroxidase(TPx) activity utilizing thioredoxin, thioredoxin reductase, and NADPH as a reducing system. Mammalian Prxs are 2030 kDa in molecular size and vary in subcellularlocalization: PrxI, II, and VI in cytosol; PrxIII in mitochondria; PrxIV in ER and secretion; PrxV shows complicated distribution including peroxisome, mitochondria and cytosol.