Neural stem cell (NSC) is the progenitor of the neural system with the character of self-renew and hav-ing the potential to differentiate into all the phenotypes in the central nervous system (CNS). NSC may serve as a source of cell transplantation for the treatment of neurodegenerative diseases to replace degenerative neurons. In this study, NSCs derived from E12.5 rat mesencephalon were main-tained and expanded using a serum-free defined medium containing basic fibroblast growth factor (bFGF) and epi-dermal growth factor (EGF). While proliferating, the cells were immunoreactive for nestin and remained multipotent to generate neurons, astrocytes, and oligodendrocytes. After 15 times passage the total number of the cell expanded about 2.4×104 fold. Compared with untreated cultures, ascorbic acid (AA) treatment led to more dopaminergic (DAergic) differentitiation as indicated by the expression of tyrosine hydroxylase (TH). With the concentration increasing, more TH+ neurons were obtained. 100 mmol/L AA could lead to a increase more than 20-fold, and a concentration of 10 靘ol/L could lead to nearly 5-fold increase in TH+ cells. However, the ratio of TH+ cells was not improved any longer with the AA increasing above the concentration of 100 靘ol/L. The results demonstrate that expanded NSCs can be induced to differentiate into dopamine neurons in vitro, which can pro-vide enough cell population for the cell transplantation, as a main intervention for the neurodegenerative diseases such as Parkinson抯 disease. Neural stem cell (NSC) is the progenitor of the neural system with the character of self-renew and hav-ing the potential to differentiate into all the phenotypes in the central nervous system (CNS). NSC may serve as a source of cell transplantation for the treatment of neurodegenerative diseases to replace degenerative neurons. In this study, NSCs derived from E12.5 rat mesencephalon were main-tained and expanded using a serum-free defined medium containing basic fibroblast growth factor (bFGF) and epi-dermal growth factor (EGF). While proliferating, the cells were immunoreactive for nestin and remained multipotent to generate neurons, astrocytes, and oligodendrocytes. After 15 times passage the total number of the cell expanded about 2.4 × 104 fold. Compared with untreated cultures, ascorbic acid ( AA) treatment led to more dopaminergic (DAergic) differentitiation as indicated by the expression of tyrosine hydroxylase (TH). With the concentration increasing, more TH + neurons were obta ined. 100 mmol / L AA could lead to a increase more than 20-fold, and a concentration of 10 靘 ol / L could lead to nearly 5-fold increase in TH + cells. However, the ratio of TH + cells was not improved any longer with the AA increasing above the concentration of 100 靘 ol / L. The results demonstrate that expanded NSCs can be induced to differentiate into dopamine neurons in vitro, which can pro-vide enough cell population for the cell transplantation, as a main intervention for the neurodegenerative diseases such as Parkinson’s disease.