Objective: To explore the DNA damage of brain cells of rat after formaldehyde exposure. Methods: Rat brain cells were exposed to different concentrations of liquid formaldehyde (0.005, 0.025, 0.125 and 0.625 mmol/L) for lh. Single cell gel electrophoresis technique (comet assay) was used to test the DNA damage of the brain cells. Result: Formaldehyde could significantly cause DNA strands breakage at concentrations of 0.005 and 0.025 mmol/L while crosslinks were induced at concentrations of 0.125 and 0.625 mmol/L. Conclusions: Formaldehyde is the both a DNA strands breaker and crosslink agent to the brain in vivo.