Formaldehyde (HCHO) generates reactive oxygen species (ROS) that induce DNA base modifications and DNA strand breaks and contributes to mutagenesis and other pathological processes. DNA non-homologous end-joining (NHEJ), a major mechanism for repairing DNA double-stranded breaks (DSB) in mammalian cells, involves the formation of a Ku protein heterodimer and recruitment of a DNA-dependent protein kinase catalytic subunit (DNA-PKcs) to the site of DNA damage. HCHO treatment induced DSB and decreased the protein expressions of Ku 70 and phosphorylated DNA-PKcs. Triphlorethol-A reduced DNA strand breaks and restored the expression of NHEJ-related proteins. In response to oxidative DNA base damage, 8-oxoguanine DNA glycosylase 1 (OGG1) plays a vital role in repair of 8-hydroxy-2'-deoxyguanosine (8-OhdG) via the base-excision repair (BER) process. In this study, HCHO significantly increased 8-OhdG levels, whereas triphlorethol-A lowered 8-OhdG levels. Suppression of 8-OhdG formation by triphlorethol-A was related to enhanced OGG1 protein expression. Triphlorethol-A also enhanced the expression of phosphorylated Akt (the active form of Akt), a regulator of OGG1, which was found to be decreased by HCHO treatment. The phosphoinositol 3-kinase (PI3K)-specific inhibitor LY294002 abolished the cytoprotective effects induced by triphlorethol-A, suggesting that OGG1 restoration by triphlorethol-A is involved in the PI3K/Akt pathway. These results suggest that triphlorethol-A may protect cells against HCHO-induced DNA damage via enhancement of NHEJ and BER capacity.