The backs with a hair cut of 6-week-old healthy ICR male mice were once exposed to a dose of $400mJ/cm^2$ UVB. An acute dermal inflammation was observed, and the inflamed skins were almost completely cured after 6 days of the exposure. At 24 hours after exposure, the epidermal keratinocytes showed a cell-membrane damage with the destruction of intercellular junctions, agglutination of tonofilaments within the cytoplasm and nucleus damage. The activity of XO showed a significant increase (p<0.05) in up to 144 hours. The activities of CAT and SOD showed a significant decrease (p<0.05) in up to 96 hours, but they were not significantly different from the normal value at 144 hours. The GST activity was significantly decreased (p<0.01) in up to 96 hours, not so at 24 hours. However, that was not significantly different from the normal value at 144 hours. There was a significant decrease (p<0.01) in the contents of TBARS at 48 and 96 hours, without any significant difference at 144 hours. While the content of GSH was significantly lower (p<0.05) at 24 hours, that was not significantly different thereafter up to 144 hours from the normal value. Therefore, it is assumed that skin damage with a dose of $400mJ/cm^2$ UVB irradiation might be caused by the oxidative stress which was resulted from the unbalance of oxygen fret radical generating and scavenging enzymes.