Polysialic acid (polySia, PSA) is a polymer of sialic acid with a degree of polymerization (DP) ranging from 8 to 400 and is mainly attached to neural cell adhesion molecule (NCAM) in brains of vertebrates . PolySia is expressed in brains during embryonic and post-neonatal development and mostly disappears in adult brains, although expression levels of NCAM remain unchanged. In adult, polySia-NCAM expression is observed in distinct regions where neural plasticity and remodeling of neural connections or neural generation are ongoing, such as the hippocampus, and olfactory system . Due to its bulky and polyanionic natures, polySia has an anti-adhesive effect on cell-cell interactions mediated by homophilic and heterophilic bindings of NCAM and other CAMs . Recently, we have newly demonstrated that polySia functions as a reservoir of neurological active molecules such as BDNF , FGF2 , and dopamine.