Objective To explore the effects of homocysteine (Hcy) on neural stem cell (NSC) proliferation and the mRNA expression level of Notch1 and Hes1 related Notch signaling pathway from neonatal rats in vitro. Methods NSCs from neonatal rats were cultured by serum-free culture method in vitro. Cells were divided into four groups: control group (Hcy-C), low dose Hcy (Hcy-L) group, middle dose Hcy (Hcy-M) group and high dose Hcy (Hcy-H) group. NSCs were iden- tified by immunofluorescent staining using the antibodies against Nestin, β-tubulin Ⅲ and GFAP. The proliferation ability of NSCs was detected by MTT. The mRNA expressions of Notch1 and Hes1 were detected by Real-time PCR. Results In the serum free suspension medium, neurospheres that consisted of a great number of nestin-positive cells were found. β-tu- bulin Ⅲ positive neurons and GFAP positive astrocytes were detected by immunofluorescence staining on the 6 th day of cell induction. MTT assay showed that the cell viability was significantly lower in three Hcy treatment groups than those of con- trol group (P ＜ 0.05). And the effect of concentration-dependent was observed. The results of RT-PCR showed that mRNA expression of Hes1 was significantly lower in three Hcy treatment groups than that in control group (P ＜ 0.05). The mRNA ex- pression of Notch1 was significantly lower in Hcy-H group than that of other three groups (P ＜ 0.05). The mRNA expression of Notch1 was significantly lower in Hcy-M group than that of Hcy-L group and control group (P ＜ 0.05). Conclusion Hcy could inhibit the proliferation of NSCs by down-regulating mRNA expression levels of Notch1 and Hes1 genes related to Notch signal pathway.