A certain concentration of formaldehyde can cause protein misfolding, cell death and biological dysfunction. Though it has been reported that formaldehyde has cytotoxicity, how formaldehyde affects cell cycle of neural cells and the molecular mechanism still needs to be clarified. In this study, neuroblastoma cell line SH-SY5Y was utilized to incubate with formaldehyde and the effect of formaldehyde on cell cycle was in formaldehyde concentration-dependent manner. No significant changes in cell cycle could be detected when [FA]≤0.1 mmol/L (cells were incubated for 48 h), while the percentages of cells in S phase and G2/M phase were markedly increased with the elevation of formaldehyde concentration (0.1 mmol/L <[FA]≤0.2 mmol/L). In the medium with 0.3 mmol/L formaldehyde, 46.28% of cells were in S phase while only 16.05% of them were in G2/M phase, that is, cell proliferation was obviously inhibited under the conditions. When cells were synchronized at G2/M phase, formaldehyde (0.1～0.3 mmol/L) could markedly increase the number of cells in S phase, though, to some extent, the number of cells in G2/M phase decreased. When cells were synchronized at S phase, 0.1 mmol/L formaldehyde could decrease the number of cells in G2/M phase, while 0.3 mmol/L formaldehyde could markedly decrease the number of cells in G2/M phase and significantly increase that in S phase. In the presence of formaldehyde, primary neurons of SD rat exhibited similar changes in cell cycle as that in SH-SY5Y cells. Furthermore, early and late apoptosis was markedly observed when 0.1 mmol/L≤[FA]≤0.2 mmol/L, while DNA were obviously damaged and most cells were apoptosis and some of them underwent necrosis when [FA]≥0.3 mmol/L. In sum, formaldehyde at a low concentration (0.1 mmol/L≤[FA]≤0.2 mmol/L) mainly suppresses DNA synthesis in S phase via hypermethylation of global DNA, while formaldehyde at a higher concentration ([FA]≥ 0.3 mmol/L) causes DNA damage, both of them lead to the aberrant effects on cell cycle.