Abstract: Objective To study the effect of folate on neural stem cells(NSCs)proliferation via MARK signal pathway in fetal rats in vitro.Methods NSCs of fetal Sprague-Dawley rat from E14d to E16d were cultured,divided into four groups which were control group,folate-deficiency group,folate-low group and folate-high group.NSCs were collected after being cultrured 6 d.The proliferation of NSCs was detected by BrdU in corporating method and immunohistochemistry method.The level of pERK1/2 expression were detected by western blot method.Results The percentage of Nestin and BrdU positive cells in total cells(x±s)in folate-low group(70.5±2.7)and folate-high group(78.8±6.9)was significantly higher than that in control group((64.2±8.9),P<0.05).The levels of pERK1(x±s)in folate-low group(0.407 ±0.018)and folate-high group(01443±01019)were higher than those in control group((0.388±0.011),P<0.05),and the levels of pERK2 in folate-low group(0.547±0.044)and folate-high group(0.563±0.041)were higher than those in control group((0.507±0.018),P<0.05).Conclusion Folate could promote proliferation of fetal NSCs via MAPK signal pathway.