Abstract: The single cell gel electrophoresis assay was applied to detect the occurrence of DNA single strand breaks in rat keratinocytes after exposed to the two main components of oxidation hair dyes-pphenylenediamine(PPD)and hydrogen peroxide(H₂O₂)and their mixture.The results showed that exposure of rat keratinocytes to the samples could cause DNA single strand breaks of the cells.Dose-responsive relatonships between exposure and the extent of DNA strand breaks(r_H2O3=0.978,r_PPD=0.993,r_H2O2=01996) were found.These results showed that the keratinocyte cytotoxicity of oxidation hair2dyes might be considered as a result form its capacity to cause DNA strand breaks,and they also explored the genotoxicity mechanism of oxidatoin hair dyes.