Numerous experiments have demonstrated the genotoxic and mutagenic effects of formaldehyde, including DNA-protein cross-links (DPC). Histone was reported to be involved in the formation of DPC in which the epsilon-amino groups of lysine and exocyclic amino groups of DNA were thought to be cross-linked through multiple step reactions. Using mass spectrometry, the N-terminus of histone and lysine residues located in both the histone N-terminal tail and the globular fold domain were identified as binding sites for formaldehyde in the current study. The observation that only lysine residues without post-translational modification (PTM) can be attacked by formaldehyde indicates that PTM blocks the reaction between lysine and formaldehyde. Additionally, we found that formaldehyde-induced Schiff bases on lysine residues could inhibit the formation of PTM on histone, raising the possibility that formaldehyde might alter epigenetic regulation.