Formaldehyde is one of the indoor air pollutions with the characteristics of extension sources and serious biological toxicities. The kidney cells of mice were chosen as materials to evaluate the relationship between the types of damage on DNA and different doses of liquid formaldehyde by the methods of single cell gel electrophoresis (SCGE), fluorescent detection assay and KCl-SDS assay. The results demonstrated that formaldehyde could induce DNA strand breaks at the lower dose (5 μmol·L^-1), and could primarily induce DNA-DNA crosslinks...